Logical channel prioritization procedure for sidelink logical channels

ABSTRACT

A user equipment in a wireless communications system supporting direct communication between user equipments selects a sidelink destination group (ProSe destination) associated with a sidelink logical channel having a highest logical channel priority among sidelink logical channels, which have data available for transmission in a sidelink control period (SC period) and which have not previously been selected in the same SC period, wherein each of the sidelink logical channels belongs to a sidelink destination group, each of the sidelink logical channels is allocated to a logical channel group (LCG) depending on a priority of said each sidelink logical channel and on a priority of the logical channel group, and the logical channel group is defined per sidelink destination group. The user equipment allocates radio resources to sidelink logical channels belonging to the selected sidelink destination group in decreasing priority order, and transmits the data using the allocated radio resources.

BACKGROUND 1. Technical Field

The present disclosure relates to methods for allocating radio resourcesto sidelink logical channels when performing a logical channelprioritization procedure. The present disclosure is also providing theuser equipment for participating in the methods described herein.

2. Description of the Related Art

Long Term Evolution (LTE)

The specification of Long-Term Evolution (LTE) has been finalized asRelease 8 (LTE Rel. 8) as a system following the 3rd GenerationPartnership Project (3GPP) Universal Mobile Terrestrial Network. The LTEsystem represents efficient packet-based radio access that provides fullIP-based functionalities with low latency and low cost. In LTE, scalablemultiple transmission bandwidths are specified such as 1.4, 3.0, 5.0,10.0, 15.0, and 20.0 MHz, in order to achieve flexible system deploymentusing a given spectrum. In the downlink, Orthogonal Frequency DivisionMultiplexing (OFDM) based radio access was adopted because of itsinherent immunity to multipath interference (MPI) due to a low symbolrate, the use of a cyclic prefix (CP) and its affinity to differenttransmission bandwidth arrangements. Single-carrier frequency divisionmultiple access (SC-FDMA) based radio access was adopted in the uplink,since provisioning of wide area coverage was prioritized overimprovement in the peak data rate considering the restricted transmitpower of the user equipment (UE). Many key packet radio accesstechniques are employed including multiple-input multiple-output (MIMO)channel transmission techniques and a highly efficient control signalingstructure is achieved in LTE Rel. 8/9.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2 . TheE-UTRAN consists of an eNodeB, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY),Medium Access Control (MAC), Radio Link Control (RLC) and Packet DataControl Protocol (PDCP) layers that include the functionality ofuser-plane header-compression and encryption. It also offers RadioResource Control (RRC) functionality corresponding to the control plane.It performs many functions including radio resource management,admission control, scheduling, enforcement of negotiated uplink Qualityof Service (QoS), cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression ofdownlink/uplink user plane packet headers. The eNodeBs areinterconnected with each other by means of the X2 interface.

The eNodeBs are also connected by means of the Si interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g. parameters of the IP bearerservice, network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at time of intra-LTEhandover involving Core Network (CN) node relocation. It is responsiblefor authenticating the user (by interacting with the HSS). TheNon-Access Stratum (NAS) signaling terminates at the MME and it is alsoresponsible for generation and allocation of temporary identities touser equipments. It checks the authorization of the user equipment tocamp on the service provider's Public Land Mobile Network (PLMN) andenforces user equipment roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roaminguser equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots, wherein the first downlink slotincludes the control channel region (PDCCH region) within the first OFDMsymbols. Each subframe consists of a give number of OFDM symbols in thetime domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), whereineach OFDM symbol spans over the entire bandwidth of the componentcarrier. The OFDM symbols thus each consists of a number of modulationsymbols transmitted on respective subcarriers as also shown in FIG. 3 .

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g. 7 OFDM symbols) and consecutive subcarriers inthe frequency domain as exemplified in FIG. 3 (e.g. 12 subcarriers for acomponent carrier). In 3GPP LTE (Release 8), a physical resource blockthus consists of resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain (for further details onthe downlink resource grid, see for example 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)”, Section 6.2, available at www.3gpp.org, andincorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure apply to laterreleases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

In carrier aggregation available in LTE from Release 10 on, two or morecomponent carriers are aggregated in order to support wider transmissionbandwidths up to 100 MHz. Several cells in the LTE system are aggregatedinto one wider channel in the LTE-Advanced system which is wide enoughfor 100 MHz even though these cells in LTE may be in different frequencybands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the bandwidth of a component carrier do not exceed thesupported bandwidth of a LTE Rel. 8/9 cell. Not all component carriersaggregated by a user equipment may necessarily be Rel. 8/9 compatible.Existing mechanism (e.g. barring) may be used to avoid Rel-8/9 userequipments to camp on a component carrier.

A user equipment may simultaneously receive or transmit one or multiplecomponent carriers (corresponding to multiple serving cells) dependingon its capabilities. A LTE-A Rel. 10 user equipment with receptionand/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain using the 3GPP LTE (Release8/9) numerology. It is possible to configure a 3GPP LTE-A (Release 10)compatible user equipment to aggregate a different number of componentcarriers originating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may currently not be possible toconfigure a mobile terminal with more uplink component carriers thandownlink component carriers.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time preserve orthogonality of the subcarriers with15 kHz spacing. Depending on the aggregation scenario, the n*300 kHzspacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

LTE Layer 2—User Plane and Control Plane Protocol Stack

The LTE layer 2 user-plane/control-plane protocol stack includes threesublayers as shown in FIG. 4 , PDCP, RLC and MAC. At the transmittingside, each layer receives a Service Data Unit, SDU, from a higher layerfor which the layer provides a service and outputs a PDU to the layerbelow. The RLC layer receives packets from the PDCP layer. These packetsare called PDCP PDUs from a PDCP point of view and represent RLC SDUsfrom an RLC point of view. The RLC layer creates packets which areprovided to the layer below, i.e. the MAC layer. The packets provided byRLC to the MAC layer are RLC PDUs from an RLC point of view and MAC SDUsfrom a MAC point of view.

At the receiving side, the process is reversed, with each layer passingSDUs up to the layer above, where they are received as PDUs.

While the physical layer essentially provides a bitpipe, protected byturbo-coding and a cyclic redundancy check (CRC), the link-layerprotocols enhance the service to upper layers by increased reliability,security and integrity. In addition, the link layer is responsible forthe multi-user medium access and scheduling. One of the main challengesfor the LTE link-layer design is to provide the required reliabilitylevels and delays for Internet Protocol (IP) data flows with their widerange of different services and data rates. In particular, the protocolover-head must scale. For example, it is widely assumed that voice overIP (VoIP) flows can tolerate delays on the order of 100 ms and packetlosses of up to 1 percent. On the other hand, it is well-known that TCPfile downloads perform better over links with low bandwidth-delayproducts. Consequently, downloads at very high data rates (e.g., 100Mb/s) require even lower delays and, in addition, are more sensitive toIP packet losses than VoIP traffic.

Overall, this is achieved by the three sublayers of the LTE link layerthat are partly intertwined.

The Packet Data Convergence Protocol (PDCP) sublayer is responsiblemainly for IP header compression and ciphering. In addition, it supportslossless mobility in case of inter-eNB handovers and provides integrityprotection to higher layer-control protocols.

The radio link control (RLC) sublayer includes mainly ARQ functionalityand supports data segmentation and concatenation. The latter twominimize the protocol overhead independent of the data rate.

Finally, the medium access control (MAC) sublayer provides HARQ and isresponsible for the functionality that is required for medium access,such as scheduling operation and random access. FIG. 5 exemplary depictsthe data flow of an IP packet through the link-layer protocols down tothe physical layer. The figure shows that each protocol sublayer addsits own protocol header to the data units.

Uplink Access Scheme for LTE

For uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. During each time interval, NodeB assigns users a unique time/frequency resource for transmitting userdata, thereby ensuring intra-cell orthogonality. An orthogonal access inthe uplink promises increased spectral efficiency by eliminatingintra-cell interference. Interference due to multipath propagation ishandled at the base station (Node B), aided by insertion of a cyclicprefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BWgrant during one time interval, e.g. asub-frame of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a sub-frame, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is however possible to assign a frequency resourceBWgrant over a longer time period than one TTI to a user byconcatenation of sub-frames.

UL Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines which UE(s) is (are) allowed to transmit, whichphysical channel resources (frequency), and the transport format(Modulation Coding Scheme (MCS)) to be used by the mobile terminal fortransmission.

The allocation information is signaled to the UE via a scheduling grant,sent on the L1/L2 control channel (called “uplink grant channel” in thefollowing). A scheduling grant message contains information which partof the frequency band the UE is allowed to use, the validity period ofthe grant, and the transport format the UE has to use for the upcominguplink transmission. The shortest validity period is one sub-frame.Additional information may also be included in the grant message for theUE, depending on the selected scheme. The UE then distributes theallocated resources among its radio bearers according to some rules. TheeNB decides the transport format based on some information, e.g.reported scheduling information and QoS info, and the UE has to followthe selected transport format. Since the scheduling of radio resourcesis the most important function in a shared-channel access network fordetermining Quality of Service, there are a number of requirements thatshould be fulfilled by the UL scheduling scheme for LTE in order toallow for an efficient QoS management.

-   -   Starvation of low priority services should be avoided.        Starvation means that the data from the low-priority logical        channels cannot be transmitted because the data from        high-priority logical channels take up all the MAC PDU space;    -   Clear QoS differentiation for radio bearers/services should be        supported by the scheduling scheme;    -   The UL reporting should allow fine granular buffer reports (e.g.        per radio bearer or per radio bearer group) in order to allow        the eNB scheduler to identify for which Radio Bearer/service        data is to be sent;    -   It should be possible to make clear QoS differentiation between        services of different users; and    -   It should be possible to provide a minimum bit rate per radio        bearer.

As can be seen from the above list, one essential aspect of the LTEscheduling scheme is to provide mechanisms with which the operator cancontrol the partitioning of its aggregated cell capacity between theradio bearers of the different QoS classes.

Logical Channel Prioritization, LCP, Procedure

For the uplink the process by which a UE creates a MAC PDU to transmitusing the allocated radio resources is fully standardized; this isdesigned to ensure that the UE satisfies the QoS of each configuredradio bearer in a way which is optimal and consistent between differentUE implementations. Based on the uplink transmission resource grantmessage signaled on the PDCCH, the UE has to decide on the amount ofdata for each logical channel to be included in the new MAC and, ifnecessary, also to allocate space for a MAC Control Element.

In constructing a MAC PDU with data from multiple logical channels, thesimplest and most intuitive method is the absolute priority-basedmethod, where the MAC PDU space is allocated to logical channels indecreasing order of logical channel priority. This is, data from thehighest priority logical channel are served first in the MAC PDU,followed by data from the next highest priority logical channel,continuing until the MAC PDU space runs out. Although the absolutepriority-based method is quite simple in terms of UE implementation, itsometimes leads to starvation of data from low-priority logicalchannels.

In LTE, a Prioritized Bit Rate (PBR) is defined for each logicalchannel, in order to transmit data in order of importance but also toavoid starvation of data with lower priority. The PBR is the minimumdata rate guaranteed for the logical channel. Even if the logicalchannel has low priority, at least a small amount of MAC PDU space isallocated to guarantee the PBR. Thus, the starvation problem can beavoided by using the PBR.

Constructing a MAC PDU with PBR consists of two rounds. In the firstround, each logical channel is served in decreasing order of logicalchannel priority, but the amount of data from each logical channelincluded in the MAC PDU is initially limited to the amount correspondingto the configured PBR value of the logical channel. After all logicalchannels have been served up to their PBR values, if there is room leftin the MAC PDU, the second round is performed. In the second round, eachlogical channel is served again in decreasing order of priority. Themajor difference for the second round compared to the first round isthat each logical channel of lower priority can be allocated with MACPDU space only if all logical channels of higher priority have no moredata to transmit.

A MAC PDU may include not only the MAC SDUs from each configured logicalchannel but also a MAC CE (Control Elements). Except for a Padding BSR(Buffer Status Report), the MAC CE has a higher priority than a MAC SDUfrom the logical channels because it controls the operation of the MAClayer. Thus, when a MAC PDU is composed, the MAC CE, if it exists, isthe first to be included, and the remaining space is used for MAC SDUsfrom the logical channels. Then, if additional space is left and it islarge enough to include a BSR, a Padding BSR is triggered and includedin the MAC PDU.

The Logical Channel Prioritization for uplink is standardized e.g. in3GPP TS 36.321, “Evolved Universal Terrestrial Radio Access (E-UTRA);Medium Access Control (MAC) protocol specification”, (latest versionv12.4.0) in Section 5.4.3.1, available at www.3gpp.org, and incorporatedherein.

The Logical Channel Prioritization (LCP) procedure is applied when a newtransmission of a transport block is performed (i.e. not atretransmissions of the same data).

RRC controls the scheduling of uplink data by signaling for each logicalchannel:

-   -   priority where an increasing priority value indicates a lower        priority level;    -   prioritisedBitRate which sets the Prioritized Bit Rate (PBR);        and    -   bucketSizeDuration which sets the Bucket Size Duration (BSD).

The UE shall maintain a variable Bj for each logical channel j. Bj shallbe initialized to zero when the related logical channel is established,and incremented by the product PBR×TTI duration for each TTI, where PBRis Prioritized Bit Rate of logical channel j. However, the value of Bjcan never exceed the bucket size, and if the value of Bj is larger thanthe bucket size of logical channel j, it shall be set to the bucketsize. The bucket size of a logical channel is equal to PBR*BSD, wherePBR and BSD are configured by upper layers.

The UE (MAC entity) shall perform the following Logical ChannelPrioritization procedure when a new transmission is performed:

-   -   The UE (MAC entity) shall allocate resources to the logical        channels in the following steps:        -   Step 1: All the logical channels with Bj>0 are allocated            resources in a decreasing priority order. If the PBR of a            radio bearer is set to “infinity”, the UE shall allocate            resources for all the data that is available for            transmission on the radio bearer before meeting the PBR of            the lower priority radio bearer(s);        -   Step 2: the UE (MAC entity) shall decrement Bj by the total            size of MAC SDUs served to logical channel j in Step 1,            NOTE: The value of Bj can be negative; and        -   Step 3: if any resources remain, all the logical channels            are served in a strict decreasing priority order (regardless            of the value of Bj) until either the data for that logical            channel or the UL grant is exhausted, whichever comes first.            Logical channels configured with equal priority should be            served equally.    -   The UE (MAC entity) shall also follow the rules below during the        scheduling procedures above:        -   The UE (MAC entity) should not segment an RLC SDU (or            partially transmitted SDU or retransmitted RLC PDU) if the            whole SDU (or partially transmitted SDU or retransmitted RLC            PDU) fits into the remaining resources;        -   if the UE (MAC entity) segments an RLC SDU from the logical            channel, it shall maximize the size of the segment to fill            the grant as much as possible;        -   the UE (MAC entity) should maximize the transmission of            data; and        -   if the UE (MAC entity) is given an UL grant size that is            equal to or larger than 4 bytes while having data available            for transmission, the UE (MAC entity) shall not transmit            only padding BSR and/or padding (unless the UL grant size is            less than 7 bytes and an AMD PDU segment needs to be            transmitted).

The UE shall not transmit data for a logical channel corresponding to aradio bearer that is suspended (the conditions for when a radio beareris considered suspended are defined in 3GPP TS 36.331, 12.5.0, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Radio Resource Control(RRC); Protocol specification”, available at www.3gpp.org).

For the Logical Channel Prioritization procedure, the UE shall take intoaccount the following relative priority in decreasing order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR or Extended PHR, or Dual        Connectivity PHR;    -   data from any Logical Channel, except data from UL-CCCH; and    -   MAC control element for BSR included for padding.

When the UE is requested to transmit multiple MAC PDUs in one TTI, steps1 to 3 and the associated rules may be applied either to each grantindependently or to the sum of the capacities of the grants. Also theorder in which the grants are processed is left up to UE implementation.It is up to the UE implementation to decide in which MAC PDU a MACcontrol element is included when the UE is requested to transmitmultiple MAC PDUs in one TTI.

Buffer Status Reporting

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesubframes. They are transmitted on the PDCCH using the C-RNTI of the UE.Dynamic scheduling is efficient for services types in which the trafficis bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one subframe, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each subframe. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Buffer status reports (BSR) from the UE to the eNodeB are used to assistthe eNodeB in allocating uplink resources, i.e. uplink scheduling. Forthe downlink case, the eNB scheduler is obviously aware of the amount ofdata to be delivered to each UE; however, for the uplink direction,since scheduling decisions are done at the eNB and the buffer for thedata is in the UE, BSRs have to be sent from the UE to the eNB in orderto indicate the amount of data that needs to be transmitted over theUL-SCH.

Buffer Status Report MAC control elements for LTE consist of either: along BSR (with four buffer size fields corresponding to LCG IDs #0-3) ora short BSR (with one LCG ID field and one corresponding buffer sizefield). The buffer size field indicates the total amount of dataavailable across all logical channels of a logical channel group, and isindicated in number of bytes encoded as an index of different buffersize levels (see also 3GPP TS 36.321, “Evolved Universal TerrestrialRadio Access (E-UTRA); Medium Access Control (MAC) protocolspecification” v 12.4.0 Section 6.1.3.1, available at www.3gpp.org, andincorporated herewith by reference).

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

In order to be robust against transmission failures, there is a BSRretransmission mechanism defined for LTE; the retransmission BSR timeris started or restarted whenever an uplink grant is restarted; if nouplink grant is received before the retransmission BSR timer expires,another BSR is triggered by the UE.

A BSR is triggered for events, such as:

-   -   Whenever data arrives for a logical channel, which has a higher        priority than the logical channels whose buffer are non-empty        (i.e. whose buffer previously contained data);    -   Whenever data becomes available for any logical channel, when        there was previously no data available for transmission (i.e.        all buffers previously empty);    -   Whenever the retransmission BSR time expires;    -   Whenever periodic BSR reporting is due, i.e. periodicBSR timer        expires; and    -   Whenever there is a spare space in a transport block which can        accommodate a BSR.

More detailed information with regard to BSR and in particular thetriggering of same is explained in the specification 3GPP TS 36.321v12.4.0 in Section 5.4.5, available at www.3gpp.org, and incorporatedherewith by reference.

If the UE has no uplink resources allocated for including a BSR in thetransport block when a BSR is triggered, the UE sends a schedulingrequest (SR) to the eNodeB so as to be allocated with uplink resourcesto transmit the BSR. Either a single-bit scheduling request is sent overthe PUCCH (dedicated scheduling request, D-SR), or the random accessprocedure (RACH) is performed to request an allocation of an uplinkradio resource for sending a BSR.

LTE Device to Device (D2D) Proximity Services (ProSe)

Proximity-based applications may be used in areas including servicesrelated to commercial services and Public Safety that would be ofinterest to operators and users. Device-to-Device (D2D) communication isa technology component for LTE-Rel.12 which enables direct communicationbetween user terminals without the traffic passing any base station. TheDevice-to-Device (D2D) communication technology allows D2D as anunderlay to the cellular network to increase the spectral efficiency.For example, if the cellular network is LTE, all data carrying physicalchannels use SC-FDMA for D2D signaling.

D2D Communication in LTE

The D2D communication in LTE is focusing on two areas: Discovery andCommunication.

ProSe (Proximity based Services) Direct Discovery is defined as theprocedure used by the ProSe-enabled UE to discover other ProSe-enabledUE(s) in its proximity using E-UTRA direct radio signals via the PC5interface. FIG. 6 schematically illustrates a PC5 interface fordevice-to-device direct discovery between UE A and UE B. It alsoschematically illustrates a Radio Protocol Stack (AS) for ProSe DirectDiscovery including the physical layer, the L2 radio protocol (which canbe MAC) and a ProSe protocol of a “higher layer”.

In D2D communication UEs transmit data signals to each other over adirect link using the cellular resources instead of through the basestation (BS). D2D users communicate directly while remaining controlledunder the BS, i.e. at least when being in coverage of an eNB. Therefore,D2D can improve system performances by reusing cellular resources.

It is assumed that D2D operates in the uplink LTE spectrum (in the caseof FDD) or uplink sub-frames of the cell giving coverage (in case ofTDD, except when out of coverage). Furthermore, D2Dtransmission/reception does not use full duplex on a given carrier. Fromindividual UE perspective, on a given carrier D2D signal reception andLTE uplink transmission do not use full duplex, i.e. no simultaneous D2Dsignal reception and LTE UL transmission is possible.

In D2D communication when one particular UE1 has a role of transmission(transmitting user equipment or transmitting terminal), UE1 sends data,and another UE2 (receiving user equipment) receives it. UE1 and UE2 canchange their transmission and reception role. The transmission from UE1can be received by one or more UEs like UE2.

With respect to the User plane protocols, in the following part of theagreement from D2D communication perspective is given (see also 3GPP TR36.843, current version 12.0.1, “Study on LTE device to device proximityservices; Radio aspects”, Section 9.2.2, available at www.3gpp.orgincorporated herein by reference):

PDCP:

-   -   1:M (one device transmits to M devices, M being an integer) D2D        broadcast communication data (i.e. IP packets) should be handled        as the normal user-plane data; and    -   Header-compression/decompression in PDCP is applicable for 1:M        D2D broadcast communication,    -   U-Mode is used for header compression in PDCP for D2D broadcast        operation for public safety.

RLC:

-   -   RLC UM is used for 1:M D2D broadcast communication;    -   Segmentation and Re-assembly is supported on L2 by RLC UM;    -   A receiving UE needs to maintain at least one RLC UM entity per        transmitting peer UE;    -   An RLC UM receiver entity does not need to be configured prior        to reception of the first RLC UM data unit; and    -   So far no need has been identified for RLC AM or RLC TM for D2D        communication for user plane data transmission.

MAC:

-   -   No HARQ feedback is assumed for 1:M D2D broadcast communication;    -   The receiving UE needs to know a source ID in order to identify        the receiver RLC UM entity;    -   The MAC header includes a L2 target ID which allows filtering        out packets at MAC layer;    -   The L2 target ID may be a broadcast, group cast or unicast        address:        -   L2 Groupcast/Unicast: A L2 target ID carried in the MAC            header would allow discarding a received RLC UM PDU even            before delivering it to the RLC receiver entity; and        -   L2 Broadcast: A receiving UE would process all received RLC            PDUs from all transmitters and aim to re-assemble and            deliver IP packets to upper layers;    -   MAC sub header contains LCIDs (to differentiate multiple logical        channels); and    -   At least Multiplexing/de-multiplexing, priority handling and        padding are useful for D2D.        ProSe Direct Communication Related Identities

ProSe Direct Communication Related Identities

3GPP TS 36.300, “Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN); Overalldescription; Stage 2”, current version 12.4.0, available atwww.3gpp.org, defines in Section 8.3 the following identities to use forProSe Direct Communication:

-   -   SL-RNTI: Unique identification used for ProSe Direct        Communication Scheduling;    -   Source Layer-2 ID: Identifies the sender of the data in sidelink        ProSe Direct Communication. The Source Layer-2 ID is 24 bits        long and is used together with ProSe Layer-2 Destination ID and        LCID for identification of the RLC UM entity and PDCP entity in        the receiver; and    -   Destination Layer-2 ID: Identifies the target of the data in        sidelink ProSe Direct Communication. The Destination Layer-2 ID        is 24 bits long and is split in the MAC layer into two bit        strings:        -   One bit string is the LSB part (8 bits) of Destination            Layer-2 ID and forwarded to physical layer as Sidelink            Control Layer-1 ID. This identifies the target of the            intended data in Sidelink Control and is used for filtering            of packets at the physical layer; and        -   Second bit string is the MSB part (16 bits) of the            Destination Layer-2 ID and is carried within the MAC header.            This is used for filtering of packets at the MAC layer.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID, Destination Layer-2 ID and Sidelink ControlL1 ID in the UE. These identities are either provided by higher layer orderived from identities provided by higher layer. In case of groupcastand broadcast, the ProSe UE ID provided by higher layer is used directlyas the Source Layer-2 ID, and the ProSe Layer-2 Group ID provided byhigher layer is used directly as the Destination Layer-2 ID in the MAClayer.

Radio Resource Allocation for Proximity Services

From the perspective of a transmitting UE, a Proximity-Services-enabledUE (ProSe-enabled UE) can operate in two modes for resource allocation:

Mode 1 refers to the eNB-scheduled resource allocation, where the UErequests transmission resources from the eNB (or Release-10 relay node),and the eNodeB (or Release-10 relay node) in turn schedules the exactresources used by a UE to transmit direct data and direct controlinformation (e.g. Scheduling Assignment). The UE needs to beRRC_CONNECTED in order to transmit data. In particular, the UE sends ascheduling request (D-SR or Random Access) to the eNB followed by abuffer status report (BSR) in the usual manner (see also followingchapter “Transmission procedure for D2D communication”). Based on theBSR, the eNB can determine that the UE has data for a ProSe DirectCommunication transmission, and can estimate the resources needed fortransmission.

On the other hand, Mode 2 refers to the UE-autonomous resourceselection, where a UE on its own selects resources (time and frequency)from resource pool(s) to transmit direct data and sidelink controlinformation (i.e. SA). One resource pool is defined e.g. by the contentof SIB18, namely by the field commTxPoolNormalCommon, this particularresource pool being broadcast in the cell, and then commonly availablefor all UEs in the cell still in RRC_Idle state. Effectively, the eNBmay define up to four different instances of said pool, respectivelyfour resource pools for the transmission of SA messages and direct data.However, a UE shall always use the first resource pool defined in thelist, even if it was configured with multiple resource pools for Release12 LTE. Later versions of the standard may handle differently.

As an alternative, another resource pool can be defined by the eNB andsignaled in SIB18, namely by using the field commTxPoolExceptional,which can be used by the UEs in exceptional cases.

What resource allocation mode a UE is going to use is configurable bythe eNB. Furthermore, what resource allocation mode a UE is going to usefor D2D data communication may also depend on the RRC state, i.e.RRC_IDLE or RRC_CONNECTED, and the coverage state of the UE, i.e.in-coverage, out-of-coverage. A UE is considered in-coverage if it has aserving cell (i.e. the UE is RRC_CONNECTED or is camping on a cell inRRC_IDLE).

-   -   The following rules with respect to the resource allocation mode        apply for the UE:    -   If the UE is out-of-coverage, it can only use Mode 2;    -   If the UE is in-coverage, it may use Mode 1 if the eNB        configures it accordingly; and    -   If the UE is in-coverage, it may use Mode 2 if the eNB        configures it accordingly.

When there are no exceptional conditions, UE may change from Mode 1 toMode 2 or vice-versa only if it is configured by eNB to do so. If the UEis in-coverage, it shall use only the mode indicated by eNBconfiguration unless one of the exceptional cases occurs;

-   -   The UE considers itself to be in exceptional conditions e.g.        while T311 or T301 is running; and    -   When an exceptional case occurs the UE is allowed to use Mode 2        temporarily even though it was configured to use Mode 1.        While being in the coverage area of an E-UTRA cell, the UE shall        perform ProSe Direct Communication Transmission on the UL        carrier only on the resources assigned by that cell, even if        resources of that carrier have been pre-configured e.g. in UICC        (Universal Integrated Circuit Card).

For UEs in RRC_IDLE the eNB may select one of the following options:

-   -   The eNB may provide a Mode 2 transmission resource pool in SIB.        UEs that are authorized for ProSe Direct Communication use these        resources for ProSe Direct Communication in RRC_IDLE; and    -   The eNB may indicate in SIB that it supports D2D but does not        provide resources for ProSe Direct Communication. UEs need to        enter RRC_CONNECTED to perform ProSe Direct Communication        transmission.

For UEs in RRC_CONNECTED:—A UE in RRC_CONNECTED that is authorized toperform ProSe Direct Communication transmission, indicates to the eNBthat it wants to perform ProSe Direct Communication transmissions whenit needs to perform ProSe Direct Communication transmission:

-   -   The eNB validates whether the UE in RRC_CONNECTED is authorized        for ProSe Direct Communication transmission using the UE context        received from MME; and    -   The eNB may configure a UE in RRC_CONNECTED by dedicated        signaling with a Mode-2 resource allocation transmission        resource pool that may be used without constraints while the UE        is RRC_CONNECTED. Alternatively, the eNB may configure a UE in        RRC_CONNECTED by dedicated signaling with a Mode 2 resource        allocation transmission resource pool which the UE is allowed to        use only in exceptional cases and rely on Mode 1 otherwise.

The resource pool for Scheduling Assignment when the UE is out ofcoverage can be configured as below:

-   -   The resource pool used for reception is pre-configured; and    -   The resource pool used for transmission is pre-configured.

The resource pool for Scheduling Assignment when the UE is in coveragecan be configured as below:

-   -   The resource pool used for reception is configured by the eNB        via RRC, in dedicated or broadcast signaling;    -   The resource pool used for transmission is configured by the eNB        via RRC if Mode 2 resource allocation is used;    -   The SA resource pool used for transmission is not known to the        UE if Mode 1 resource allocation is used; and    -   The eNB schedules the specific resource(s) to use for Scheduling        Assignment transmission if Mode 1 resource allocation is used.        The specific resource assigned by the eNB is within the resource        pool for reception of Scheduling Assignment that is provided to        the UE.

FIG. 7 illustrates the use of transmission/reception resources foroverlay (LTE) and underlay (D2D) system.

Basically, the eNodeB controls whether UE may apply the Mode 1 or Mode 2transmission. Once the UE knows its resources where it can transmit (orreceive) D2D communication, it uses the corresponding resources only forthe corresponding transmission/reception. For example, in FIG. 7 , theD2D subframes will only be used to receive or transmit the D2D signals.Since the UE as a D2D device would operate in Half Duplex mode, it caneither receive or transmit the D2D signals at any point of time.Similarly, the other subframes illustrated in FIG. 7 can be used for LTE(overlay) transmissions and/or reception.

Transmission Procedure for D2D Communication

The D2D data transmission procedure differs depending on the resourceallocation mode. As described above for Mode 1, the eNB explicitlyschedules the resources for the Scheduling Assignment and the D2D datacommunication after a corresponding request from the UE. Particularly,the UE may be informed by the eNB that D2D communication is generallyallowed, but that no Mode 2 resources (i.e. resource pool) are provided;this may be done e.g. with the exchange of the D2D communicationInterest Indication by the UE and the corresponding response, D2DCommunication Response, where the corresponding exemplaryProseCommConfig information element mentioned above would not includethe commTxPoolNormalCommon, meaning that a UE that wants to start directcommunication involving transmissions has to request E-UTRAN to assignresources for each individual transmission. Thus, in such a case, the UEhas to request the resources for each individual transmission, and inthe following the different steps of the request/grant procedure areexemplarily listed for this Mode 1 resource allocation:

-   -   Step 1: UE sends SR (Scheduling Request) to eNB via PUCCH;    -   Step 2: eNB grants UL resource (for UE to send BSR) via PDCCH,        scrambled by C-RNTI;    -   Step 3: UE sends D2D BSR indicating the buffer status via PUSCH;    -   Step 4: eNB grants D2D resource (for UE to send data) via PDCCH,        scrambled by D2D-RNTI; and    -   Step 5: D2D Tx UE transmits SA/D2D data according to grant        received in step 4.

A Scheduling Assignment (SA) is a compact (low-payload) messagecontaining control information, e.g. pointer(s) to time-frequencyresources for the corresponding D2D data transmissions. The content ofthe SA is basically in accordance with the grant received in Step 4above. The exact details of the D2D grant and SA content are not fixedyet but as a working assumption for the SA content the followingagreements were achieved:

-   -   Frequency resource is indicated by Rel-8 UL Type 0 resource        allocation (5-13 bits depending on System BW);    -   1 bit frequency hopping indicator (as per Rel-8):        -   Note that some reinterpretation of the indexing is to be            defined so that hopping does not use PRBs outside the            configured resource pool for mode 2;    -   Only single-cluster resource allocations are valid:        -   this implies that if there are gaps in the resource pool in            the frequency domain, a resource allocation shall not            straddle a gap;    -   No RV indicator in SA; and    -   RV pattern for data: {0, 2, 3, 1}.

On the other hand, for Mode 2 resource allocation, above steps 1-4 arebasically not necessary, and the UE autonomously selects resources forthe SA and D2D data transmission from the transmission resource pool(s)configured and provided by the eNB.

FIG. 8 exemplarily illustrates the transmission of the SchedulingAssignment and the D2D data for two UEs, UE-A and UE-B, where theresources for sending the scheduling assignments are periodic, and theresources used for the D2D data transmission are indicated by thecorresponding Scheduling Assignment.

FIG. 9 illustrates the D2D communication timing for Mode 2, autonomousscheduling, during one SA/data period, also known as SC period, SidelinkControl period.

FIG. 10 illustrates the D2D communication timing for Mode 1,eNB-scheduled allocation during one SA/data period. A SC period is thetime period consisting of transmission of Scheduling Assignments andtheir corresponding data. As can be seen from FIG. 9 , the UE transmitsafter an SA-offset time, a Scheduling Assignment using the transmissionpool resources for scheduling assignments for Mode 2, SA_Mode2_Tx_pool.The 1st transmission of the SA is followed e.g. by three retransmissionsof the same SA message. Then, the UE starts the D2D data transmission,i.e. more in particular the T-RPT bitmap/pattern, at some configuredoffset (Mode2data_offset) after the first subframe of the SA resourcepool (given by the SA_offset). One D2D data transmission of a MAC PDUconsists of its 1st transmissions and several retransmissions. For theillustration of FIG. 9 (and of FIG. 10 ) it is assumed that threeretransmissions are performed (i.e. 2nd, 3rd, and 4th transmission ofthe same MAC PDU). The Mode2 T-RPT Bitmap (time resource pattern oftransmission (T-RPT)) basically defines the timing of the MAC PDUtransmission (1st transmission) and its retransmissions (2nd, 3rd, and4th transmission).

During one SA/data period, the UE can transmit multiple transport blocks(only one per subframe (TTI), i.e. one after the other), however to onlyone ProSe destination group. Also the retransmissions of one transportblock must be finished before the first transmission of the nexttransport block starts, i.e. only one HARQ process is used for thetransmission of the multiple transport blocks.

As apparent from FIG. 10 , for the eNB-scheduled resource allocationmode (Mode 1), the D2D data transmission, i.e. more in particular theT-RPT pattern/bitmap, starts in the next UL subframe after the last SAtransmission repetition in the SA resource pool. As explained alreadyfor FIG. 9 , the Mode1 T-RPT Bitmap (time resource pattern oftransmission (T-RPT)) basically defines the timing of the MAC PDUtransmission (1st transmission) and its retransmissions (2nd, 3rd, and4th transmission).

ProSe Network Architecture and ProSe Entities

FIG. 11 illustrates a high-level exemplary architecture for anon-roaming case, including different ProSe applications in therespective UEs A and B, as well as a ProSe Application Server and ProSefunction in the network. The example architecture of FIG. 11 is takenfrom 3GPP TS 23.303, “Proximity-based services (ProSe); Stage 2”,v.12.3.0 Section 4.2 titled “Architectural Reference Model”, availableat www.3gpp.org, and incorporated herein by reference.

The functional entities are presented and explained in detail in theabove cited 3GPP TS 23.303 Section 4.4 titled “Functional Entities”incorporated herein by reference. The ProSe function is the logicalfunction that is used for network-related actions required for ProSe,and plays different roles for each of the features of ProSe. The ProSefunction is part of the 3GPP's EPC and provides all relevant networkservices like authorization, authentication, data handling etc. relatedto proximity services. For ProSe direct discovery and communication, theUE may obtain a specific ProSe UE identity, other configurationinformation, as well as authorization from the ProSe function over thePC3 reference point. There can be multiple ProSe functions deployed inthe network, although for ease of illustration a single ProSe functionis presented. The ProSe function consists of three main sub-functionsthat perform different roles depending on the ProSe feature: DirectProvision Function (DPF), Direct Discovery Name Management Function, andEPC-level Discovery Function. The DPF is used to provision the UE withnecessary parameters in order to use ProSe Direct Discovery and ProSeDirect Communication.

The term “UE” used in said connection refers to a ProSe-enabled UEsupporting ProSe functionality, such as:

-   -   Exchange of ProSe control information between ProSe-enabled UE        and the ProSe Function over PC3 reference point;    -   Procedures for open ProSe Direct Discovery of other        ProSe-enabled UEs over PC5 reference point;    -   Procedures for one-to-many ProSe Direct Communication over PC5        reference point;    -   Procedures to act as a ProSe UE-to-Network Relay. The Remote UE        communicates with the ProSe UE-to-Network Relay over PC5        reference point.

The ProSe UE-to Network Relay uses layer-3 packet forwarding;

-   -   Exchange of control information between ProSe UEs over PC5        reference point, e.g. for UE-to-Network Relay detection and        ProSe Direct Discovery;    -   Exchange of ProSe control information between another        ProSe-enabled UE and the ProSe Function over PC3 reference        point. In the ProSe UE-to-Network Relay case the Remote UE will        send this control information over PC5 user plane to be relayed        over the LTE-Uu interface towards the ProSe Function; and    -   Configuration of parameters (e.g. including IP addresses, ProSe        Layer-2 Group IDs, Group security material, radio resource        parameters). These parameters can be pre-configured in the UE,        or, if in coverage, provisioned by signaling over the PC3        reference point to the ProSe Function in the network.

The ProSe Application Server supports the Storage of EPC ProSe User IDs,and ProSe Function IDs, and the mapping of Application Layer User IDsand EPC ProSe User IDs. The ProSe Application Server (AS) is an entityoutside the scope of 3GPP. The ProSe application in the UE communicateswith the ProSe AS via the application-layer reference point PC1. TheProSe AS is connected to the 3GPP network via PC2 reference point.

UE Coverage States for D2D

As already mentioned before, the resource allocation method for D2Dcommunication depends apart from the RRC state, i.e. RRC_IDLE andRRC_CONNECTED, also on the coverage state of the UE, i.e. in-coverage,out-of-coverage. A UE is considered in-coverage if it has a serving cell(i.e. the UE is RRC_CONNECTED or is camping on a cell in RRC_IDLE).

The two coverage states mentioned so far, i.e. in-coverage (IC) andout-of-coverage (OOC), are further distinguished into sub-states forD2D. FIG. 12 shows the four different states a D2D UE can be associatedto, which can be summarized as follows:

-   -   State 1: UE1 has uplink and downlink coverage. In this state the        network controls each D2D communication session. Furthermore,        the network configures whether UE1 should use resource        allocation Mode 1 or Mode 2;    -   State 2: UE2 has downlink but no uplink coverage, i.e. only DL        coverage. The network broadcasts a (contention-based) resource        pool. In this state the transmitting UE selects the resources        used for SA and data from a resource pool configured by the        network; resource allocation is only possible according to Mode        2 for D2D communication in such a state;    -   State 3: Since UE3 has no uplink and downlink coverage, the UE3        is, strictly speaking, already considered as out-of-coverage        (OOC). However, UE3 is in the coverage of some UEs which are        themselves (e.g. UE1) in the coverage of the cell, i.e. those        UEs can be also referred as CP-relay UEs. Therefore, the area of        the state-3 UEs in FIG. 12 can be denoted as CP UE-relay        coverage area. UEs in this state 3 are also referred to as        OOC-state-3 UEs. In this state the UEs receive some cell        specific information which is sent by the eNB (SIB) and        forwarded by the CP UE-relay UEs in the coverage of the cell via        PD2DSCH to the OOC-state-3 UEs. A (contention-based)        network-controlled resource pool is signaled by PD2DSCH; and    -   State 4: UE4 is out of coverage and does not receive PD2DSCH        from other UEs which are in the coverage of a cell. In this        state, which is also referred to as state-4 OOC, the        transmitting UE selects the resources used for the data        transmission from a pre-configured pool of resources.

The reason to distinguish between state-3 OOC and state-4 OOC is mainlyto avoid potentially strong interference between D2D transmissions fromout-of coverage devices and legacy E-UTRA transmissions. In generalD2D-capable UEs will have preconfigured resource pool(s) fortransmission of D2D SAs and data for use while out of coverage. If theseout-of-coverage UEs transmit on these preconfigured resource pools nearcell boundaries, then, interference between the D2D transmissions andin-coverage legacy transmissions could have a negative impact oncommunications within the cell. If D2D-enabled UEs within coverageforwarded the D2D resource pool configuration to those out-of-coveragedevices near the cell boundary, then, the out-of-coverage UEs couldrestrict their transmissions to the resources specified by the eNode Band therefore minimize interference with legacy transmissions incoverage. Thus, RAN1 introduced a mechanism where in-coverage UEs areforwarding resource pool information and other D2D relatedconfigurations to those devices just outside the coverage area (state-3UEs).

The Physical D2D synchronization channel (PD2DSCH) is used to carry thisinformation about in-coverage D2D resource pools to the UEs in networkproximity, so that resource pools within network proximity are aligned.The detailed content of the PD2DSCH is not finalized yet though.

LCP Procedure for D2D, Sidelink, Logical Channels

The LCP procedure for D2D will be different than the above-presented LCPprocedure for “normal” LTE data. The following information is taken fromR2-145435, a Change Request 0744 for TS 36.321 in its version 12.3.0directed at the Introduction of ProSe and its functionality; it isincorporated herewith in its entirety by reference.

The Logical Channel Prioritization procedure is applied when a newtransmission is performed.

The UE shall perform the following Logical Channel Prioritizationprocedure when a new transmission is performed. The UE shall allocateresources to the sidelink logical channels according to the followingrules:

-   -   the UE should not segment an RLC SDU (or partially transmitted        SDU) if the whole SDU (or partially transmitted SDU) fits into        the remaining resources;    -   if the UE segments an RLC SDU from the sidelink logical channel,        it shall maximize the size of the segment to fill the grant as        much as possible;    -   the UE should maximize the transmission of data; and    -   if the UE is given an sidelink grant size that is equal to or        larger than 10 bytes while having data available for        transmission, the UE shall not transmit only padding.

NOTE: The rules above imply that the order by which the sidelink logicalchannels are served is left for UE implementation. Generally, for onePDU, MAC shall consider only logical channels with the same SourceLayer-2ID—Destination Layer 2 ID pairs, i.e. for one PDU, the MAC entityin the UE shall consider only logical channels of the same ProSedestination group. Furthermore, in Rel-12 during one SA/data period theD2D transmitting UE can only transmit data to one ProSe destinationgroup.

All D2D (sidelink) logical channels, e.g. STCH, Sidelink TrafficChannel, are allocated to the same logical channel group (LCG) withLCGID set to ‘11’. In Rel-12 there is no prioritization mechanism forD2D (sidelink) logical channels/groups. Essentially, all sidelinklogical channels have the same priority from UE point of view, i.e. theorder by which the sidelink logical channels are served is left for UEimplementation.

Buffer Status Reporting for ProSe

The (D2D) sidelink Buffer Status Reporting procedure is used to providethe serving eNB with information about the amount of sidelink dataavailable for transmission in the sidelink buffers of the UE. RRCcontrols sidelink BSR reporting by configuring the two timersPeriodic-ProseBSR-Timer and RetxProseBSR-Timer. Each sidelink logicalchannel (STCH) is allocated to an LCG with LCGID set to “11” and belongsto a ProSe Destination group.

A sidelink Buffer Status Report (BSR) shall be triggered if someparticular events occurs, as given section 5.14.1.4 of TS 36.321,v.12.5.0. Section 6.1.3.1.a of TS 36.321, v.12.5.0 specifies the ProSeBSR MAC Control Elements and their corresponding content as follows.

The ProSe Buffer Status Report (BSR) MAC control element consists of onegroup index field, one LCG ID field and one corresponding Buffer Sizefield per reported D2D destination group. More in detail, for eachincluded ProSe destination group, the following fields are defined:

-   -   Group index: The group index field identifies the ProSe        destination group. The length of this field is 4 bits. The value        is set to the index of the destination identity reported in        ProseDestinationInfoList;    -   LCG ID: The Logical Channel Group ID field identifies the group        of logical channel(s) which buffer status is being reported. The        length of the field is 2 bits and it is set to “11”;    -   Buffer Size: The Buffer Size field identifies the total amount        of data available across all logical channels of a ProSe        Destination group after all MAC PDUs for the TTI have been        built. The amount of data is indicated in number of bytes; and    -   R: Reserved bit, set to “0”.

FIG. 13 shows the ProSe BSR MAC control element for even N (number ofProSe destination groups), taken from the above cited TS 36.321,v.12.5.0.

Mission Critical Push To Talk

Recently, a service called Mission Critical Push To Talk (MCPTT) servicehas been studied in 3GPP, which is also captured in 3GPP TS 22.179,v.13.1.0, “Mission Critical Push to Talk (MCPTT) over LTE; Stage 1”,available at www.3gpp.org. A Push To Talk (PTT) service provides anarbitrated method by which two or more users may engage incommunication. Users may request permission to transmit (e.g.,traditionally by means of a press of a button). The Mission CriticalPush To Talk over LTE (MCPTT) service supports an enhanced PTT service,suitable for mission critical scenarios, based upon 3GPP Evolved PacketSystem (EPS) services. The requirements for MCPTT service defined withincan also form the basis for a non-mission critical Push To Talk (PTT)service. The MCPTT Service is intended to support communication betweenseveral users (a group call), where each user has the ability to gainaccess to the permission to talk in an arbitrated manner. However, theMCPTT Service also supports Private Calls between pairs of users. TheMCPTT Service builds on the existing 3GPP transport communicationmechanisms provided by the EPS architectures to establish, maintain, andterminate the actual communication path(s) among the users.

The MCPTT Service also builds upon service enablers: GCSE_LTE and ProSe.To the extent feasible, it is expected that the end user's experience tobe similar regardless if the MCPTT Service is used under coverage of anEPC network or based on ProSe without network coverage. To clarify thisintent, the requirements are grouped according to applicability toon-network use, off-network use, or both. The MCPTT Service allows usersto request the permission to talk (transmit voice/audio) and provides adeterministic mechanism to arbitrate between requests that are incontention (i.e., Floor control). When multiple requests occur, thedetermination of which user's request is accepted and which users'requests are rejected or queued is based upon a number ofcharacteristics (including the respective priorities of the users incontention). MCPTT Service provides a means for a user with higherpriority (e.g., emergency condition) to override (interrupt) the currenttalker. MCPTT Service also supports a mechanism to limit the time a usertalks (holds the floor) thus permitting users of the same or lowerpriority a chance to gain the floor.

The MCPTT Service provides the means for a user to monitor activity on anumber of separate calls and enables the user to switch focus to achosen call. An MCPTT Service user may join an already established MCPTTGroup call (Late call entry). In addition the MCPTT Service provides theUser ID of the current speaker(s) and user's Location determinationfeatures. The users of an MCPTT Service may have more stringentexpectations of performance than the users of a commercial PTT service.

An MCPTT Service provides Group Call and Private Call capabilities,which have various process flows, states and permissions associated withthem. FIGS. 14 , FIG. 15 , and FIG. 16 indicate the high level flows,states and permissions associated with Group Calls and Private Calls.The diagrams apply to the on-network case and off-network case, as froma user perspective the service and concepts should appear similar on thenetwork and off the network. From a technical perspective there might bedifferences between the on-network states and off-network states (e.g.,off the network Affiliation might not require notifying an applicationserver of a user's affiliation and there might also be other differencesin the detail depending on the extent to which the off-networkcapabilities can match the on-network capabilities).

If an MCPTT User wants to communicate with an MCPTT Group they have tobe allowed to access the MCPTT Group (i.e., be an MCPTT Group Member),they then have to affiliate and then can have an MCPTT Group as theirSelected MCPTT Group. If an MCPTT User is only affiliated to a groupthis is so that they can receive from the group, however if an MCPTTUser has a Selected MCPTT Group this is their group for transmitting on.The differences in states enable an MCPTT User to receive from multipleMCPTT Groups, but specify which MCPTT Group they would like to transmiton.

In particular, FIGS. 14, 15 and 16 show respective MCPTT user statediagrams for a user which has allowed both receiving and transmittingwith respect to a particular MCPTT group, a user that is only allowed totransmit and a user that is only allow to receive. In the present stateof discussions, this diagram serves merely for illustrative purposes anddoes not supersede the requirements. It is not exhaustive and does notinclude all the different scenarios.

It is possible for an MCPTT User to be affiliated with one or more MCPTTGroups. Normally, while in operation, an MCPTT User informs the MCPTTService about which MCPTT Groups he would like to be affiliated to.These affiliations remain in effect until the MCPTT User removes them,or changes them, or signs out of the service. Some MCPTT Users havepermanent affiliations to certain MCPTT Groups and those affiliationsare set up implicitly (i.e., automatically) when operating on thenetwork. For those users, the MCPTT Group affiliation starts when theMCPTT Service successfully signs in the user and ends when the MCPTTUser's explicit or implicit (e.g., due to inactivity or the turning offof all its devices) request to sign out of the MCPTT Service isacknowledged.

Every time a PTT request is granted a user can start an MCPTTtransmission or “talk burst”. An MCPTT Group Call consists of one ormore MCPTT transmissions. Whether two consecutive transmissions fromsame or different users are part of the same call, or the secondtransmission starts a new call, depends on the configurable maximumlength of the inactivity period between the consecutive MCPTTtransmissions. This inactivity period can be seen as a Hang Time thatstarts at the end of the preceding transmission. While this timer isrunning, the resources associated with the call stay assigned to thecall (except in case of pre-emption), which could reduce the latency offuture floor requests for this group versus groups who are not involvedin a call. When a new transmission starts during the inactivity period,the timer is stopped, reset and restarted again at the end of thattransmission.

The MCPTT Service recognizes a number of “special” group callsincluding: Broadcast Group Call, Emergency Group Call and Imminent Perilgroup call.

MCPTT Priority Model

Many LTE non-public safety users today subscribe to one particularpriority and QoS level of service (e.g., “gold”, “silver” or “bronze”),which always provides fixed differentiation. This model, effective andrelatively straightforward for non-public safety users, falls short whenit comes to the needs of the public safety applications.

MCPTT Priority and QoS is situational. The MCPTT Service is intended toprovide a real-time priority and QoS experience for MCPTT calls, aspublic safety users have significant dynamic operational conditions thatdetermine their priority. For example, the type of incident a responderis serving or the responder's overall shift role needs to stronglyinfluence a user's ability to obtain resources from the LTE system.

The MCPTT Priority handling for on-network use for MCPTT Calls isconceptually modeled as shown in FIG. 17 . The conceptual modelidentifies three areas of prioritization: prioritization between andwithin calls, inter-system prioritization, and prioritization at thetransport layer (EPS and UE). At the Application Layer a generic,network side, functional entity, “MCPTT Priority and QoS Control”,processes with each request static, preconfigured information aboutusers and groups participating in MCPTT, as well as dynamic (orsituational) information about them. Based on the results of thisprocessing, the “MCPTT Priority and QoS Control” provides information toand directs interactions with other functional entities, systems, orlayers to ensure, to the extent possible, that from a quality ofexperience point of view, calls and transmissions are handled properlyin accordance to established policy rules.

In FIG. 17 , User Static Attributes include information categorizing theuser, possibly by several criteria (e.g., first responder, secondresponder, supervisor, dispatcher, administrator), as well asjurisdictional boundaries and possibly a preconfigured system-wideindividual priority level.

The Group Static Attributes include information about the nature/type ofthe group and the owning organization(s), the jurisdictional boundariesfor transmitters and receivers within the group, the normal hours ofoperation for the group, pre-emption dispositions relative to othergroups, and the default minimum priority of the group.

The User Dynamic Attributes include the user/Participant's operationalstatus (e.g., on/off duty), his location, the type of incident (e.g.,MCPTT Emergency or Imminent Peril) he might be involved in and whetheror not he initiated it, whether or not he is individually involved in aformally managed incident and if yes, the boundaries of the incidentarea, the incident severity and his assigned role in the resolution ofthe incident.

The Group Dynamic Attributes include the type of incident (e.g., MCPTTEmergency or Imminent Peril), if any, the group is currently handlingand in case of involvement in a formally managed incident the boundariesof the incident area and the incident severity.

As shown in FIG. 18 , the higher layers for each particular bearerprovide a priority based on the real time attributes (The User StaticAttributes, The Group Static Attributes, The User Dynamic Attributes,The Group Dynamic Attributes) a priority value to the MAC layer.

MAC layer may further use this in at least two possible ways:

A) As part of LCP mechanism i.e. together with the Logical Channeland/or destination group priority; and

B) Independently (before/after LCP) to make a go/no-go decision: in thiscase Logical Channel Prioritization would decide on how much data towhich logical channel is allocated (in which group(s)) and then MCPTTpriority only reflects in floor arbitration.

At present, the particular procedure for prioritizing logical channelsin a UE is not defined.

SUMMARY

One non-limiting and exemplary embodiment provides an improved methodfor allocating radio resources to logical channels when performing alogical channel prioritization procedure in a user equipment forProximity Services.

In one general aspect, the techniques disclosed here feature a userequipment operable in a wireless communications system supporting directcommunication between user equipments, including: a storage with asidelink configuration stored and specifying a plurality of destinationgroups, each destination group including possible destinations forsidelink data as well as storing a logical channel priority for eachlogical channel out of logical channels configured for the sidelinkdestination groups; and a scheduling unit that: selects a sidelinkdestination group with a sidelink logical channel having sidelink dataavailable for transmission with the highest logical channel priorityamong the sidelink logical channels having data available fortransmission; and allocates radio resources to the sidelink logicalchannels belonging to the selected sidelink destination group indecreasing priority order.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9);

FIG. 4 illustrates the layer 2 user and control-plane protocol stackcomposed of the three sublayers, PDCP, RLC and MAC;

FIG. 5 gives an overview of the different functions in the PDCP, RLC andMAC layers as well as illustrates exemplary the processing of SDUs/PDUsby the various layers;

FIG. 6 schematically illustrates a PC 5 interface for device-to-devicedirect discovery;

FIG. 7 illustrates the use of transmission/reception resources foroverlay (LTE) and underlay (D2D) systems;

FIG. 8 illustrates the transmission of the Scheduling Assignment and theD2D data for two UEs;

FIG. 9 illustrates the D2D communication timing for the UE-autonomousscheduling Mode 2;

FIG. 10 illustrates the D2D communication timing for the eNB-scheduledscheduling Mode 1;

FIG. 11 illustrates an exemplary architecture model for ProSe for anon-roaming scenario;

FIG. 12 illustrates that coverage regarding four different states theD2D UE can be associated to;

FIG. 13 illustrates the ProSe Buffer Status Reporting MAC ControlElement defined in the standard;

FIG. 14 illustrates the association between ProSe logical channels,ProSe LCGs, and ProSe destination groups for an exemplary scenario;

FIG. 15 illustrates a MCPTT user state diagram for a user which hasallowed both receiving and transmitting with respect to a particularMCPTT group;

FIG. 16 illustrates a MCPTT user state diagram for a user which hasallowed only transmitting with respect to a particular MCPTT group;

FIG. 17 illustrates a MCPTT user state diagram for a user which hasallowed only receiving with respect to a particular MCPTT group;

FIG. 18 shows a conceptual on-network MCPTT priority model;

FIG. 19 shows schematically integration of priorities in the layermodel;

FIG. 20 illustrates the relationship between different ProSe LCGs andProSe destination groups according to a particular variant of the secondembodiment;

FIG. 21 illustrates the possible mappings between ProSe LCHs and ProSeLCGs for a particular association between ProSe LCHs and ProSedestination groups according to the particular variant of the secondembodiment illustrated in FIG. 20 ;

FIG. 22 illustrates the relationship between different ProSe LCGs andProSe destination groups according to another particular variant of thesecond embodiment;

FIG. 23 illustrates the possible mappings between ProSe LCHs and ProSeLCGs for the same particular association between ProSe LCHs and ProSedestination groups as in FIG. 21 according to the particular variant ofthe second embodiment illustrated in FIG. 22 ;

FIG. 24 illustrates the ProSe Buffer Status Reporting MAC ControlElement according to a variant of the second embodiment;

FIG. 25 is a flow diagram illustrating an exemplary method forprioritization according to the fifth embodiment;

FIG. 26 is a flow diagram illustrating an exemplary method for prioritysetting for logical channels;

FIG. 27 is a flow diagram illustrating an exemplary method forsupporting flow control by suspending/resuming logical channels;

FIG. 28 is a flow diagram illustrating an exemplary method forperforming flow control based on priorities;

FIG. 29 is a schematic drawing illustrating a format of a sidelinkcontrol information;

FIG. 30 is a schematic drawing illustrating a format of a MAC PDU;

FIG. 31 is a schematic drawing illustrating a message flow implementingan exemplary floor control mechanism for a group of three UEs;

FIG. 32 is a schematic drawing illustrating a message flow implementingan exemplary floor control mechanism for a group of three UEs; and

FIG. 33 is a block diagram illustrating an example of a user equipmentimplementing the prioritization of logical channels.

DETAILED DESCRIPTION

A mobile station or mobile node or user terminal or user equipment is aphysical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The term “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency resources.

The term “ProSe” or in its unabbreviated form, “Proximity Services”,used in the set of claims and in the application is applied in thecontext of Proximity-based applications and services in the LTE systemas exemplarily explained in the background section. Other terminologysuch as “D2D” is also used in this context to refer to theDevice-to-Device communication for the Proximity Services. Furthermore,in the claims the terminology of “ProSe logical channels” is used so asto be consistent with the overall terminology employed throughout theset of claims, such as “ProSe data”, or “ProSe destination groups”;however, the different term “sidelink” is also used in this context,i.e. mostly as “sidelink logical channels”, i.e. those logical channelsset up for proximity services/D2D. The term “ProSe destination group”used in the set of claims and in the remaining application can beunderstood as e.g. one Source Layer-2 ID—Destination Layer 2 ID pairdefined in 3GPP LTE.

As explained in the background section, one major goal is tocontinuously improve the implementation of the Proximity Services in thecurrent overall LTE system. Currently, the LCP procedure for D2Dcommunication is defined such that the order by which the sidelinklogical channels are served is left for UE implementation, i.e. noprioritization mechanism for sidelink channels is supported andessentially all sidelink logical channels have the same priority from UEpoint of view. Furthermore, as currently implemented, for one MAC PDU,the MAC entity in the UE shall consider only logical channels of thesame ProSe destination group. Again, it is up to the UE implementationin which order the ProSe destination groups are served.

The currently-standardized LCP procedure entails several disadvantagesas will become apparent from below.

For example, the D2D resources are inefficiently used, and the halfduplex problem (UE cannot receive and transmit at the same time, i.e.TTI) cannot be mitigated. In more detail, to explain the problem, ascenario is assumed where several members of a particular ProSedestination group (e.g. public safety) communicate between each other.Two UEs belonging to the same ProSe destination group receive respectivegrants to transmit ProSe data. Since the selection order of the ProSedestination groups (and the sidelink logical channels) is up to the UEimplementation, the eNodeB e.g. cannot prevent these two UEs to usetheir grants for a transmission to the same ProSe destination group atthe same TTI. Consequently, the two transmitting UEs will not be able toreceive the transmission from the other transmitting UE in the same TTIsince it is transmitting at the same time (due to the half duplexoperation of ProSe). First, there is the risk that information among thegroup members differs due to said half duplex problem, i.e. it is notguaranteed that all group members receive all information. Furthermore,some of the scheduled resources are inefficiently used.

The following exemplary embodiments are conceived by the inventors tomitigate the problems explained above.

In the following, several illustrative embodiments will be explained indetail. Some of these are to be implemented in the wide specification asgiven by the 3GPP standards and explained partly in the presentbackground section, with the particular key features as explained in thefollowing pertaining to the various embodiments. It should be noted thatthe embodiments may be advantageously used for example in a mobilecommunication system, such as 3GPP LTE-A (Release 10/11/12/13)communication systems as described in the Technical Background sectionabove, but the embodiments are not limited to its use in this particularexemplary communication networks.

The explanations should not be understood as limiting the scope of thedisclosure, but as a mere example of embodiments to better understandthe present disclosure. A skilled person should be aware that thegeneral principles of the present disclosure as laid out in the claimscan be applied to different scenarios and in ways that are notexplicitly described herein. Correspondingly, the following scenariosassumed for explanatory purposes of the various embodiments shall notlimit the present disclosure and its embodiments as such. For example,it is assumed for the following embodiments that in general the ProSeLCP procedure will be used for the same purpose as currentlystandardized, i.e. for a UE to allocate available radio resources todifferent logical channels with available data for transmission whenconstructing the MAC PDU for performing a new transmission. Also, it isassumed that several ProSe destination groups are already defined in asame or similar manner as currently standardized. Furthermore, whensetting up the various ProSe logical channels, it is assumed that anassociation between the ProSe logical channels and the ProSe destinationgroups is performed in the UE, such that each ProSe logical channel setup in the UE is associated with a particular ProSe destination group towhich the ProSe data of the ProSe logical channel is destined.

Moreover, various embodiments discuss the LCP procedure, according towhich radio resources are distributed between the ProSe logical channelswith available data for transmission. When no further indications orrestrictions are given, it should be assumed that the radio resources tobe allocated are either eNB-scheduled resources (resource allocationMode 1) or radio resources autonomously determined by the UE from anappropriate resource pool (resource allocation Mode 2).

First Illustrative Embodiment

According to a first exemplary embodiment, a method for allocating radioresources to logical channels when performing a logical channelprioritization, LCP, procedure in a user equipment is provided forProximity Services. The method allows a UE to allocate available radioresources to the ProSe logical channels with available ProSe data whengenerating a MAC PDU for a new transmission. The ProSe logical channelsare set up appropriately in the UE, and according to the firstembodiment all the ProSe logical channels are assigned to the same ProSeLCG (“11”) as in the prior art. A main idea is to introduce aprioritization mechanism when performing the LCP procedure, which isbased on the ProSe destination groups. As explained before, a MAC PDUshall only contain ProSe data relating to one particular ProSedestination group, such that the UE must first select the ProSedestination group. This is also the case for the first embodiment, whichhowever in addition foresees that each of the ProSe destination groupsis assigned a respective priority (e.g. termed “ProSe destination grouppriority”).

The ProSe destination group priority may be different to the logicalchannel priority which is used in LTE within the LCP procedure for thegeneration of MAC PDUs transmitted on the Uu interface. As described inthe technical background section for LTE uplink transmission on the Uuinterface basically data of all logical channels can be multiplexed intoa MAC PDU, the logical channel priority determines the order in whichthe logical channels are served. However for ProSe communication onlydata of logical channels which are assigned to the same ProSedestination group can be mapped in a ProSe PDU.

The assigning of the respective priorities to the ProSe destinationgroups can be e.g. performed by a higher-layer entity in the network,i.e. a corresponding ProSe function or entity which is responsible insaid respect. For instance, said ProSe function/entity could be the sameas the one that already sets up and manages the ProSe destinationgroups. As explained in the background section in connection with FIG.15 , such a ProSe entity could be the ProSe Function defined therein. Insaid case, the information on the ProSe destination groups and theirpriorities are distributed to other entities in the network, such as theProSe-enabled UEs which can be performed directly via the PC3 interface,and/or such as the eNodeB. For example, the ProSe function/entitytransmits information on the ProSe destination groups (such as ID)together with the assigned ProSe destination groups by some higher-layerprotocol

Furthermore, this information can be provided to the eNB(s) of theE-UTRAN first. The eNodeBs, instead of the ProSE function in turn caninform the UEs.

Alternatively, the ProSe destination group priorities may also bealready pre-configured in the UE (and the eNB) (e.g. by the standard, orstored in the UICC), such that corresponding information does not haveto be signaled over the network but is already available at the UE (andthe eNB) from the beginning.

Furthermore, there are also several possibilities on how the actualpriority levels available for the ProSe destination groups can beimplemented. It is currently discussed that about 8 different ProSedestination groups can be configured for a UE. Consequently, one variantof the first embodiment would then provide a corresponding number of 8different priority levels, encoded by 3 bits, where e.g. priority level1 is the highest and priority level 8 is the lowest priority, or viceversa. For example, a ProSe destination group for public safety willhave a high priority. However, there may be also less priority levelsthan ProSe destination groups. Furthermore, the various embodimentsdiscussed herein based on the ProSe destination group priorities are notlimited thereto, and any other suitable prioritization of the ProSedestination groups is possible.

The first embodiment implements a prioritization mechanism for the LCPprocedure based on the above-discussed ProSe destination grouppriorities. In more detail, a first step is introduced according towhich the UE, at the time when ProSe data is available and acorresponding MAC PDU shall be generated for a new transmission, selectsone of the ProSe destination groups according to its priority, such thatthe MAC PDU to be generated and transmitted will only include ProSe dataof ProSe logical channels destined to said selected ProSe destinationgroup. For example, the UE selects that ProSe destination group with thehighest priority. It should be noted that only those ProSe destinationgroups are considered for which data is actually available; i.e. ProSedestination groups, e.g. of higher priority, but without data to betransmitted, are disregarded.

As assumed before, radio resources are available for the UE to transmitdata in D2D direct communication to another ProSe UE via the PC5interface, be it Mode 1 or Mode 2 allocated resources. Correspondingly,in the second step, the UE shall allocate the available radio resourcesto the ProSe logical channels (e.g. STCHs), but only considers thoseProSe logical channels that belong to the selected ProSe destinationgroup. However, how exactly, e.g. in which order, the UE serves thevarious ProSe logical channels of said selected ProSe destination groupis then left for the respective UE implementation, and is not specifiedin further detail at this point. It should be noted in said respect thatall ProSe logical channels within said ProSe destination group have thesame priority (which is changed according to the second embodiment, aswill be explained later).

The MAC PDU is thus constructed with ProSe data of only said selected,high-priority, ProSe destination group.

In said respect, it should be noted that the MAC PDU cannot includeProSe data of two different ProSe destination groups, ascurrently-standardized. Consequently, even if radio resources are stillavailable after all ProSe logical channels of the selected ProSedestination group are served (i.e. if there is room left in the MACPDU), no further ProSe data of other ProSe logical channels can beincluded; e.g. the MAC PDU is filled with padding or ProSe MAC CE ifexisting.

The thus generated MAC PDU can then be further processed and transmittedin the usual manner. For instance, depending on the resource allocationmode, the transmission of the MAC PDU, and previously of thecorresponding SA message, can be performed as explained in thebackground section, e.g. in connection with FIGS. 15 and 16 .

As a further optional improvement to the first embodiment, the UE shouldfurther consider the following rules when performing the LCP procedure:

-   -   the UE should not segment an RLC SDU (or partially transmitted        SDU) if the whole SDU (or partially transmitted SDU) fits into        the remaining resources;    -   if the UE segments an RLC SDU from the sidelink logical channel,        it shall maximize the size of the segment to fill the grant as        much as possible;    -   the UE should maximize the transmission of data.    -   if the UE is given an sidelink grant size that is equal to or        larger than 10 bytes while having data available for        transmission, the UE shall not transmit only padding.

These optional rules are taken from the currently-standardized LCPprocedure as presented in the background section, and can be likewiseused for the improved/assisted LCP procedure of the first embodiment(also for the second and third embodiments).

The advantage achieved by the first embodiment is that the selection ofthe ProSe destination group is not left up to the UE implementation.Rather, by appropriately assigning priorities to the different ProSedestination groups and having the UE select the ProSe destination groupbased on the assigned priority, the UE behavior is predetermined in saidrespect, and thus foreseeable (for the eNB e.g.). Correspondingly, theeNB can use this foreseeable UE behavior to improve its scheduling (wheneNB-scheduled resource allocation Mode 1 is used), and thus e.g. tomitigate the half-duplex problem. In particular, the eNB would notschedule two UEs for the same TTI if they have the same ProSedestination group as having the highest priority. In the above-discussedscenario when explaining the half-duplex problem, the eNB would thusonly schedule one of the two UEs, and the other UE e.g. in the next or asubsequent TTI, so as to avoid that the two UEs transmit at the sametime to the same ProSe destination group. Radio resources are no longerwasted, and can thus be used/scheduled more efficiently.

Furthermore, important ProSe data (such as for important ProSedestination groups, such as public safety, police, etc.) will not bedelayed unnecessarily since the corresponding ProSe destination grouppriorities will be set high, and will thus be served preferentially inthe UE when performing the LCP procedure, as presented above.

According to a variant of the first embodiment, the selection of theProSe destination group based on their ProSe destination group priorityis improved further, by taking into account the previous LCPprocedure(s). In other words, the ProSe destination groups are notserved strictly by decreasing order of their ProSe destination grouppriority, but there may be exceptions when considering previous LCPprocedures such that delay and/or starvation of lower-priority ProSedestination groups is avoided.

The step of selecting that ProSe destination group among the ProSedestination groups with available data with the highest priority amongthem can be repeated at each time instance where a new transmission isto be performed, i.e. each time an LCP procedure is performed. In saidcase, one and the same ProSe destination group, having the highestpriority among them, is selected every time, assuming that ProSe data isalways available for said ProSe destination group. This can lead tosignificant delays and starvation of ProSe destination groups with lowerpriority, aggravated by the current standardization which requires thatduring one SA/data period (for which the LCP procedure is performed) theUE can transmit only to one ProSe destination group. Thus, even ifunused resources would be available at some point during the SA/dataperiod after serving that ProSe destination group with the highestpriority, they could not be used for ProSe data destined to other ProSedestination groups.

In order to avoid the disadvantages for such scenarios, a variant of thefirst embodiment improves the first prioritization mechanism by avoidingthat a particular ProSe destination group is repeatedly served for aprolonged time when ProSe data is likewise available for other,lower-priority, ProSe destination groups.

In more detail, the step of selecting that ProSe destination group amongthe ProSe destination groups with available data with the highestpriority among them is not performed as such for a case where in aprevious LCP (or in a LCP performed some predetermined time ago) thatsame ProSe destination group with the highest priority was alreadyserved, even though ProSe data (old or new) for this ProSe destinationgroup is available for transmission when performing this subsequent LCPprocedure. In such a case, that already-served ProSe destination groupis momentarily disregarded for the LCP procedure, such that effectivelythe ProSe destination group among the remaining ProSe destination groupswith available data with the second-highest priority among them isselected for further proceeding with the LCP procedure.

This improved variant of the first embodiment may also be applied infuture scenarios, as will be explained below. At the moment it isstandardized that the UE has only one valid ProSe grant per SA/dataperiod, such that even if the UE would receive a second ProSe grant, itwould discard the “old” grant in favor of the new one. Furthermore,during one SA/data period, for which this ProSe grant is valid, the UEcan transmit only to one ProSe destination group. In consequence, evenif no more data is available for the initially-selected ProSedestination group, it is not possible to use unused radio resources fromthe grant to transmit data to another ProSe destination group. This is awaste of resources, and thus this may change in future releases, suchthat during one SA/data period more than one ProSe destination group canbe served and more than one ProSe grant can be received and used.Respectively for the autonomous selection (Mode 2), the UE may beallowed to select more than one SL grant for a SA/data period. Moreover,one MAC PDU may still be required to include only data for one ProSedestination group.

In such a case, where multiple ProSe MAC PDUs are to be transmitted(i.e. to multiple ProSe destination groups) and multiple ProSe grantsare available, the selection of the ProSe destination groups isperformed in a decreasing order of the ProSe destination group priority.In detail, the first ProSe grant is used during a first LCP procedurefor that ProSe destination group with available data with the highestpriority among them. However, the second ProSe grant is used during asecond LCP procedure for that ProSe destination group with availabledata with the second-highest priority among them, even if there isremaining data available to be transmitted to the ProSe destinationgroup with the highest priority among them. And so on for any furtherProSe destination groups and ProSe grants.

Second Illustrative Embodiment

Although the first embodiment already provides various advantages overthe corresponding LCP procedure of the prior art, the inventors haveidentified further disadvantages.

Another problem with the prior art and also with the procedure of thefirst embodiment is that there is no guarantee that the UE servesdelay-critical services, like Voice over IP (VoIP), with the highestpriority, since the selection order of the sidelink logical channelsduring the LCP procedure is left up to the UE implementation. A wrong orun-optimized UE implementation may result in delay-critical services tosuffer large latencies and perhaps even starvation.

For illustration purposes only, the following exemplary scenario isconsidered where three ProSe logical channels, LCH #1, LCH #2, and LCH#3, are set up in the user equipment, and all three are associated withthe same ProSe LCG (e.g. “11”) as in the prior art. It is exemplarilyassumed that LCH #1 and LCH #2 are assigned to ProSe destination group1, and LCH #3 is assigned to ProSe destination group 2. This isillustrated in FIG. 20 . ProSe destination group 1 is assumed to have ahigher priority than ProSe destination group 2. ProSe data is availableto be transmitted for all three logical channels, and radio resourcesare available to be allocated by the UE.

If the various variants of the first embodiment are applied to thisscenario, the UE would first select ProSe destination group 1, forhaving the higher priority between the two ProSe destination groups forwhich data is to be transmitted. Then, since the order in which thelogical channels of selected ProSe destination group 1 are served, i.e.LCH #1 and LCH #2, is up to the UE implementation, either LCH #1 or LCH#2 is served first. Thus, if there are not enough radio resources forthe data of both LCHs, then data of one of the two ProSe LCHs will bedelayed, and in the worst case starvation may happen. This isparticularly detrimental if this happens to delay-critical services,such as VoIP. For instance, assuming that LCH #1 is carrying thedelay-critical data, if the UE decides to serve LCH #2 first, thecorrespondingly constructed MAC PDU might not contain any of the data ofthe delay-critical service or only some of it.

The variants of the second embodiment shall overcome this problem, andfor that purpose a second prioritization level is introduced as will beexplained in detail below. In the following, the second embodiment willbe explained for illustration purposes mainly as being completely basedon the first embodiment, i.e. it extends the first embodiment byadditionally implementing the second prioritization level but maintainsthe other features of the first embodiment (and its variants). However,it should be noted that the use of the secondary prioritizationmechanism can be also used stand-alone, i.e. without having the firstprioritization mechanism of selecting the ProSe destination group basedon its priority. Consequently, while the following explanation focuseson a second embodiment which indeed includes the first prioritizationmechanism of the first aspect (and all its variants explained above),the second embodiment shall not be restricted thereto but may beconsidered standalone.

The second prioritization mechanism used for the second embodimentdistinguishes between different ProSe Logical Channel Groups, ProSeLCGs, and their corresponding priority. In short, in contrast to thecurrent standardization where only one ProSe LCG (“11”) is provided forProSe logical channels (see background and e.g. FIG. 20 ), a pluralityof ProSe LCGs is defined for ProSe direct communication to which the UEmay associate the set-up ProSe logical channels. Further, each of theplurality of ProSe LCGs is assigned a respective priority, e.g. termed“ProSe LCG priority”. Then, when performing an LCP procedure, the UEtakes into account the respective priorities of the ProSe LCGs, to whichthe various ProSe logical channels belong, when allocating the availableresources between the ProSe logical channels, namely such that the ProSelogical channels are served in a decreasing order of their associatedpriority. This will be explained in more detail in the following.

There are several possibilities on how the different ProSe LCGs aredefined. Among other things, this will also depend on how the mappingbetween the ProSe logical channels and the ProSe LCG in relation to thevarious ProSe destination groups shall be implemented. Two alternativepossible mappings will be presented below, although others may beequally possible.

The two alternatives will be illustrated in connection with FIGS. 21 and23 , which shall illustrate the relationship between the ProSedestination groups and the ProSe LCGs. In both figures, it isexemplarily assumed that there are in total only four ProSe destinationgroups, i.e. with a corresponding ProSe destination group ID of 2 bits,and it is further assumed that for identifying a ProSe LCG 1 bit isavailable, 0 or 1. Respective examples are illustrated in FIGS. 22 and24 , where a different scenario is assumed with two ProSe destinationgroups and four ProSe LCGs.

The first alternative will be explained in connection with FIG. 21 ,which illustrates that each ProSe destination group can be related toany of the ProSe LCGs; in other words, the ProSe LCGs are definedirrespective of the defined ProSe destination groups. Consequently, byusing the ProSe LCG ID it is possible to distinguish between the definedProSe LCGs, i.e. ProSe LCG ID:0 identifies ProSe LCG #1, and ProSe LCGID:1 identifies ProSe LCG #2. The corresponding mapping of the ProSelogical channels to the different ProSe LCGs by the UE takes this intoaccount, and thus is independent from the ProSe destination group towhich the ProSe logical channel belongs. For instance, a UE when settingup its ProSe logical channels will assign each of them to any one of thedefined ProSe LCG as appropriate. This is exemplarily illustrated inFIG. 22 , where ProSe LCH #1 and ProSe LCH #3 are assumed to beassociated with ProSe destination group 1, and ProSe LCH #2 isassociated with ProSe destination group 2. As depicted with dashedlines, each of the ProSe logical channels can be associated with any ofthe ProSe LCGs 1-4, irrespective of their association with the ProSedestination group. Put differently, ProSe LCHs associated with differentProSe destination groups can be mapped to the same ProSe LCG (which isnot possible for the second alternative explained below).

According to the second alternative, illustrated in FIG. 23 , for eachProSe destination group different ProSe LCGs are defined. For theexemplary scenario of FIG. 23 , there may be in total 8 different ProSeLCGs, which is 4×2, where 4 relates to the total number of differentProSe destination groups, and 2 relates to the different ProSe LCGs perProSe destination group. In order to unambiguously distinguish betweenall the different ProSe LCGs, it is necessary to consider the ProSedestination group (e.g. ProSe destination group ID) in addition to theProSe LCG ID. Put differently, the ProSe LCGs are restricted tor only aparticular ProSe destination group. Correspondingly, the ProSedestination group ID alone unambiguously defines the ProSe destinationgroup, and in combination with the ProSe LCG ID provides a codepoint forunambiguously identifying the ProSe LCG. The corresponding possiblemapping of the ProSe logical channels to the different ProSe LCGs by theUE is also different from the one explained for FIGS. 21 and 22 . Asexplained above, the UE when setting up the ProSe logical channels willbe assigned for each of them a particular ProSe destination group, asappropriate. The UE may then be assigned for each of the ProSe logicalchannels only those ProSe LCGs which belong to the ProSe destinationgroup with which the logical channel is associated. This is exemplarilyillustrated in FIG. 24 , where the same association between ProSe LCHsand ProSe destination groups as for FIG. 22 is assumed. Here however,since ProSe LCHs 1 and 3 are associated with ProSe destination group 1,they can only be associated with ProSe LCGs 1 or 2, i.e. those which arethemselves associated with ProSe destination group 1 (see dashed lines).The same applies to ProSe LCH 2 which thus can only be mapped by the UEto either ProSe LCG3 or LCG 4, i.e. those which are themselvesassociated with ProSe destination group 2.

According to one variant, the different ProSe LCGs and their prioritiesmay be defined centrally, e.g. by a higher-layer entity in the network,i.e. a corresponding ProSe function or entity which shall be responsiblein said respect, e.g. the ProSe Function already presented in thebackground section in connection with FIG. 15 . In said case, theinformation on the ProSe LCGs and their priorities are distributed toother entities in the network, such as the ProSe-enabled UEs which canbe performed directly via the PC3 interface, and to the eNodeB, e.g. byuse of some higher-layer protocol.

Alternatively, the respective information on the ProSe LCGs and theirpriorities can be provided to the eNB(s) of the E-UTRAN first, whichcould in turn inform the UEs, instead of the ProSe Function directlycontacting the UEs.

Alternatively, the ProSe LCGs and their priorities may also bepre-configured in the UE (and the eNB) (e.g. by the standard or storedin the UICC), such that corresponding information does not have to besignaled in the network but is already available at the UE (and the eNB)from the beginning.

Furthermore, there are also several possibilities on how the actualpriority levels available for the ProSe LCGs can be implemented. Thismay e.g. depend on the total number of ProSe LCGs, which may varydepending on the actual implementation as explained in connection withFIG. 21-24 . For example, one variant of the second embodiment wouldthen provide the same number of priority levels as the number of ProSeLCGs, e.g. starting from priority level 1 as being the highest etc.However, there may be also less priority levels than ProSe LCGs. Anyother suitable prioritization of the ProSe LCGs is possible, too.

The ProSe LCG priorities are used in the LCP procedure of the secondembodiment for a second prioritization mechanism, which determines inwhich order the ProSe logical channels are served when allocating theavailable radio resources for constructing a MAC PDU for a newtransmission. Particularly, the ProSe logical channels have a ProSe LCGpriority associated via the ProSe LCG to which they have been mapped.According to the second prioritization, the available resources areallocated to the ProSe logical channels in a decreasing order of theircorresponding ProSe LCG priority.

The MAC PDU is thus sequentially constructed with the ProSe data fromthe ProSe logical channels in a decreasing ProSe LCG priority order.

It should be noted that ProSe logical channels which are associated withthe same ProSe LCG, will have the same priority, i.e. the same ProSe LCGpriority; the order in which these particular ProSe logical channelswith the same associated priority are served during the LCP procedure ise.g. up to the UE implementation.

The advantage of implementing said second level of prioritization basedon the ProSe LCG priorities is that a fine prioritization control ispossible for sidelink logical channels belonging to the same ProSedestination group. Since the UE behavior is predictable, the eNB canschedule more efficiently for the eNB-scheduled resource allocationMode 1. Furthermore, delay-critical data, such as VoIP, will betransported by a ProSe logical channel which the UE would map to a ProSeLCG with a correspondingly high priority. Consequently, since the LCPprocedure according to the second embodiment would take these ProSe LCGpriorities into account while allocating the resources, thedelay-critical data will be transmitted first, without any unnecessarydelay.

As mentioned above, the second prioritization level can be implementedin various variants of the first embodiment, such that there are twosubsequent levels of prioritization: in a first step the UE serves theProSe destination groups in a decreasing order of their priorities, andthen in a subsequent second step the UE serves the ProSe logicalchannels of the currently-selected (i.e. currently-served),high-priority, ProSe destination group in a decreasing order of theirassociated ProSe LCG priority.

In an alternative implementation the UE could derive, based on the ProSedestination group priorities and the ProSe LCG priorities associated tothe logical channels, a logical channel priority and serve the logicalchannels in the priority order of the logical channels. More inparticular, the priority of a logical channel would be a function of thepriority of the ProSe destination group associated with this logicalchannel and the priority of the ProSe LCG associated with this logicalchannel. In one exemplary implementation the UE could first derive thepriorities of the logical channels by using a function of the ProSedestination group priorities and ProSe LCG priorities as explainedbefore and then perform the LCP procedure similar to LTE uplink case,where logical channels are served in the logical channel priority order.

A further variant of the second embodiment provides an adapted bufferstatus reporting such that the eNB receives more detailed information.At the moment, the ProSe buffer status report provides buffer sizeinformation per ProSe destination group, which indicates the amount ofdata available across all ProSe logical channels of said ProSedestination group (see background section and FIG. 19 ). Furthermore,all sidelink logical channels are mapped to one LCG in the prior art.Consequently, the currently-standardized ProSe Buffer Status Report MACControl Element does not distinguish between data of different logicalchannels within one ProSe destination group.

According to one variant, the ProSe buffer status report provides moredetailed information, namely buffer size information per pair of ProSedestination group and ProSe LCG, the buffer size information indicatingthe amount of ProSe data across all ProSe logical channels beingassociated with said pair, i.e. associated with both the ProSedestination group and ProSe LCG of said pair.

FIG. 25 exemplarily discloses a ProSe BSR MAC control element accordingto this variant of the second embodiment, wherein for each pair of ProSedestination group and ProSe LCG, the MAC CE includes the following:

-   -   Group index: The group index field identifies the ProSe        destination group of the pair. The length of this field is 4        bits. The value is set to the index of the destination identity        reported in ProseDestinationInfoList;    -   LCG ID: The Logical Channel Group ID field identifies the ProSe        LCG of the pair (and thus identifies logical channel(s) which        buffer status is being reported). The length of the field is 2        bits;

Buffer Size: The Buffer Size field identifies the total amount of dataavailable across all logical channels of the ProSe destinationgroup-ProSe LCG pair, after all MAC PDUs for the TTI have been built.The amount of data is indicated in number of bytes;

Depending on the actual format used for the ProSe BSR MAC CE, theremight be reserved bits, set to e.g. “0”.

In the particular example taken for FIG. 25 , it is assumed that LCH #1is associated with ProSe destination group 1 and ProSe LCG 1, LCH #2 isassociated with ProSe destination group 1 and ProSe LCG 2, and LCH #3 isassociated with ProSe destination group 2 and ProSe LCG 2. Consequently,there are three pairs of ProSe destination group and ProSe LCG, namelyProSe destination group 1 with respectively ProSe LCG 1 and 2, and ProSedestination group 2 with ProSe LCG 2.

The advantage of the above-described improved ProSe BSR is that the eNBcan now distinguish between different ProSe LCGs belonging to the sameProSe destination group, which allows the eNB to provide a moreefficient scheduling.

With the above-described change with regard to the actual content of theProSe BSR, the improved ProSe buffer status reporting can beadditionally defined as in the prior art, e.g. explained in thebackground section (with reference to R2-145435, CR 0744 for TS 36.321,subclause 5.x.1.4). Only as a few examples: RRC may control the sidelinkBSR reporting by configuring the two timers Periodic-ProseBSR-Timer andRetxProseBSR-Timer; different events trigger the ProSe BSR; differenttypes of ProSe BSR exist, such as the Padding ProSe BSR, Regular andPeriodic ProSe BSR.

Third Illustrative Embodiment

The third embodiment further improves the resource allocation procedureof the UE when performing an LCP procedure. In particular, the thirdembodiment focuses on the UE-autonomous scheduling Mode 2, where the UEselects radio resources from a resource pool when needed for a newtransmission.

The third embodiment can be combined with any of the variants of thefirst and second embodiment, but can be also implemented as stand-alone.

As explained in the background section, the UE can be provided withmultiple resource pools respectively for the transmission of the SAmessage and D2D data. Thus, in the following it is assumed that aplurality of resource pools for the D2D communication in the autonomousresource allocation mode is defined for the UE, i.e. more in particulara plurality of resource pools for the transmission of the schedulingassignments (SA) and a plurality of resource pools for the correspondingD2D data transmission. This can be done e.g. by the eNB and/or by aProSe function/entity in the network, responsible in said respect. Thesepluralities of resource pools for SA and data are provided to the UEe.g. via SIB18, i.e. broadcasted in the System information of thecorresponding cell.

Correspondingly, different resource pools are available to the UE whenhaving to perform UE-autonomous resource allocation (Mode 2), i.e. whengenerating a new D2D MAC PDU. Furthermore, for the third embodiment itis assumed, as for all the variants of the first and second embodiments,that a plurality of ProSe destination groups is defined. For somevariants of the third embodiment, it may be assumed that each of theProSe destination groups is associated with a particular ProSedestination group priority; further details are already provided in thefirst and second embodiments, and are thus omitted here.

In order to further improve the resource allocation by the UE when inMode 2, after the UE selects that ProSe destination group with ProSedata available for transmission (e.g. with the highest priority amongthem), the appropriate resource pool (more in particular a resource poolfor transmission of the scheduling assignment and a resource pool forthe corresponding data) among the various resource pools is selected bythe UE based on the selected ProSe destination group. Put differently,the UE selects radio resource pools (for SA and data) which areappropriate for the selected ProSe destination group. This selection ofthe radio resource pool(s) can be implemented in different ways, two ofwhich will be presented in the following.

According to the first variant, a new mapping between ProSe destinationgroups and resource pools is introduced, such that each ProSedestination group is assigned a resource pool for SA and a resource poolfor D2D data. This mapping can be defined e.g. by a ProSefunction/entity in the network, responsible in said respect. In saidcase, the information on the mapping is transmitted to the UE (and theeNB) e.g. by use of some higher-layer protocol. Alternatively, thismapping can be pre-configured in the UE (and the eNB) (e.g. by thestandard, or stored in the UICC), such that the corresponding mappingdoes not need to be signaled over the network, but is already availableat the UE (and the eNB).

In any case, based on the selected ProSe destination group, the UE maythen simply select that resource pool, respectively resource pools (onefor SA and one for the corresponding D2D data) which is associated tothe selected ProSe destination group, based on the stored mappinginformation. Since within one SA/data period, also referred to asSidelink Control (SC) period, a D2D UE can only transmit D2D MAC PDUs toone ProSe destination group, the selection of the resource pool(s) needsto be done only once per SA/data period.

According to the second variant, instead of providing an explicitmapping, the UE shall determine the appropriate radio resource pool forthe selected ProSe destination group differently. In particular, each ofthe plurality of resource pools is assigned a particular priority, e.g.termed resource pool priority.

There are also several possibilities on how the actual priority levelsavailable for the plurality of resource pools are implemented. Thesecond variant foresees that the priorities of the ProSe destinationgroups and the resource pools shall be compared to appropriately selecta resource pool based on the selected ProSe destination group.Consequently, the two priorities shall be defined in such a manner thatthey are comparable in a meaningful manner. An example given before forthe priorities of the ProSe destination groups assumed 8 differentpriority levels, with priority level 1 as being the highest and prioritylevel 8 being the lowest. Correspondingly, the priority of the resourcepools can be defined and assigned in a similar manner, such that aresource pool which should only be used for important data, is assigneda high priority (e.g. 1), and a resource pool which can already be usedfor less important data, is assigned a low priority (e.g. 8).

These resource pool priorities and the assigning of the priorities couldbe done e.g. by the same ProSe function/entity in the network, which wasalready responsible for setting up the plurality of resource pools. Insaid case, the information of the priority level of a particular radioresource pool could be signaled together with the information on theparticular radio resource pool itself; e.g. in the pool configurationsignaled in SIB 18.

Alternatively, the priorities could be pre-configured in the UE (and theeNB) (e.g. by the standard or stored in the UICC), in the same manner asthe mappings for the first variant of the third embodiment.

In any case, according to the second variant, the UE is configured witha plurality of resource pools (respectively for SA and D2D data), eachof which has assigned a particular priority level. As mentioned above,the priorities of the resource pools are defined such that only data ofsidelink logical channels belonging to a ProSe destination group with agroup priority same (or higher) than the priority associated to theresource pool can be transmitted with radio resources from said resourcepool.

Correspondingly, after the UE selected a ProSe destination group (basedon the ProSe destination group priority), the UE compares the priorityof the selected ProSe destination group with the priority of the variousresource pools, and selects that resource pool (one for SA and one forD2D data) having a pool priority that is the same or lower than theProSe destination group priority of the selected ProSe destinationgroup.

Correspondingly, the UE can determine a sidelink grant based on radioresources of the selected radio resource pool. The radio resources ofthe determined sidelink grant can then be used and allocated to thevarious ProSe logical channels according to the LCP procedure discussedfor various variants of the first and second embodiments.

The advantage of having a resource pool selection mechanism is that theUE behavior for the selecting a resource pool for Scheduling assignmentand corresponding data transmission is predictable from eNodeB point ofview. This allows eNodeB to control the load on the different resourcepools. Furthermore, the interference situation could differ for thedifferent resource pools, such that the ProSe data transmissionexperiences a different Quality of Service (QoS).

Alternatively, different resource pools could be defined for differentcyclic prefix (CP) lengths, i.e. one of the plurality of the resourcepools for the D2D transmission shall use the extended CP length, whereasother resource pools for the D2D transmission shall use the normal CPlength.

In the following, the sequence of steps is briefly explained when thethird embodiment is combined with the basic variant of the secondembodiment. Accordingly, it is assumed that the UE is in scheduling Mode2 (UE-autonomous). In a first step, the UE shall determine the ProSedestination group for which it wants to transmit D2D data in this TTI,respectively SA/data period, based on the ProSe destination grouppriority (e.g. the one having the highest among them). Then, the UEdetermines the corresponding resource pool based on the selected ProSedestination group (either based on the mapping information, or based onthe priority comparison explained above). Based on the selected radioresource pool, the UE will select a sidelink grant from the selectedradio resource pool and assign said radio resources of the grant to theProSe logical channels of the selected ProSe destination group in adecreasing order of the ProSe LCG priority associated with the ProSelogical channels.

The third embodiment can however also be applied to the eNB-scheduledresource allocation mode (Mode 1), assuming that the plurality ofresource pools are also available for the UE when being scheduled inMode 1. In particular, in future releases the plurality of resourcepools currently being defined for Mode 2 only, may become also usablefor Mode 1 scheduling, such that the UE needs to be instructed to whichresource pool the eNB-scheduled grant, received from the eNB, actuallyrefers.

Consequently, according to this variant of the third embodiment, whenthe UE receives a sidelink grant from the eNB, it performs the improvedLCP procedure as explained above in connection with the first and secondembodiments. However, in order to apply the eNB grant, it will selectthat resource pool based on the selected ProSe destination group(according to any of the various variants already discussed for thethird embodiment in connection with the improved Mode 1 resource poolselection).

Further Illustrative Embodiments

In the following different embodiments will be explained that can becombined with any of the variants of the first, second, and thirdembodiments explained above, but which may also be consideredstandalone, i.e. independently from any of the first, second, and thirdembodiments.

For one additional embodiment, it is assumed that it is possible to use,i.e. configure, both resource allocation modes (i.e. Mode 1 and Mode 2)at the same time, in contrast to the presently standardizedimplementation where the UE is configured with only one resourceallocation mode. In said case, the resource allocation mode can be madee.g. logical channel specific, such that some logical channels areconfigured for scheduled resource allocation mode, whereas other logicalchannels are configured for autonomous resource allocation mode. The UEmay be configured e.g. by the eNB via RRC signaling, in said respect.

Alternatively the resource allocation mode of a ProSe logical channelcould be configured e.g. by the same ProSe function/entity in thenetwork, which was already responsible for assigning the differentpriorities of the ProSe destination group respectively ProSe LCGs andsignaled to the UE respectively eNodeB by higher layer protocol.

Alternatively, the resource allocation mode associated to ProSe logicalchannel could be pre-configured in the UE (and the eNB) (e.g. by thestandard or stored in the UICC), in the same manner as the mappings forthe first variant.

In consequence, the LCP procedure performed in the UE would then e.g.only consider those logical channels which are configured for theeNB-scheduled resource allocation mode in case the sidelink grant isreceived from eNB, and conversely the UE would then only consider thoselogical channels which are configured for UE-autonomous resourceallocation mode in case the side link grant is determined by the UEautonomously from a resource pool (without an eNB grant). Thus, in afirst step of the LCP procedure, those logical channels that do notrefer to the same resource allocation mode as the currently-processedsidelink grant would be disregarded for the LCP procedure. Therefore,e.g. no radio resources would be allocated thereto. And, whenconsidering the first embodiment, the step of selecting the ProSedestination group would be performed as if these disregarded logicalchannels would not be part of the ProSe destination group(s). Similarly,when considering the second embodiment, these disregarded logicalchannels, and their associated ProSe LCG priority, would be ignored whendetermining the order of logical channels with which the resources areallocated.

Furthermore, the UE would only report data of those logical channelsconfigured for the eNB-scheduled resource allocation mode in thecorresponding ProSe BSR.

Alternatively, the resource allocation mode could be made specific ofthe ProSe destination group, or of the ProSe Logical Channel group.

For another additional embodiment, it is assumed that semi-persistentscheduling is supported for D2D, and thus radio resources of said SPSgrant shall be allocated to ProSe logical channels according to the LCPprocedure. According to this additional embodiment, data of the ProSedestination group with the highest priority among the ProSe destinationgroups with available data shall be transmitted; i.e. when generating anew MAC PDU to be transmitted using SPS resources, the highest-priorityProSe destination group is selected for further proceeding with the LCPprocedure. Consequently, the SPS resources are allocated to only thoseProSe logical channels being associated with the selected ProSedestination group.

Alternatively, particular ProSe destination groups can be(pre-)configured for SPS or not, such that the UE, when allocating SPSresources, may choose from only those ProSE destination groups that areconfigured for SPS. The configuration can be done e.g. by higher layersignaling, e.g. by using a flag that indicates that the correspondingProSe destination group is intended for SPS. Alternatively, this SPSconfiguration of the ProSe destination groups can be pre-configured inthe UE.

One of the advantages achieved by the LCP procedure of the first aspectis that ProSe data for high-priority ProSe destination groups aretransmitted first, and are not delayed unnecessarily as in the prior artsystem. The different priority levels can be appropriately assigned tothe different ProSe destination groups by a central ProSefunction/entity so as to achieve the desired effect.

In summary, a second prioritization level is implemented for the LCPprocedure, in addition to the first prioritization level based on theProSe destination group priorities discussed in connection with thefirst aspect. In more detail, instead of providing only one LogicalChannel Group, LCG, in connection with ProSe communication as in theprior art, the second aspect is based on a plurality of ProSe LCGs, eachof which is associated with one out of a plurality of differentpriorities, termed e.g. ProSe LCG priority. According to one variant,the ProSe LCGs, and also the corresponding ProSe LCG priorities, can beset up and managed by a ProSe function/entity in the network responsiblein said respect. In said case, information on the available ProSe LCGsand their corresponding priority levels can be transmitted to the UE andfor example also to the eNB so as to further allow the eNB to improveits scheduling of radio resources for said user equipment. The UE shallthen map each of its plurality of configured ProSe logical channels(e.g. STCHs) to one out of the plurality of ProSe LCGs.

When ProSe data is to be transmitted and provided that a sidelink grantis available (either signaled by eNB or determined by the UEautonomously from a resource pool), the improved LCP procedure of thesecond aspect, being an extension to the improved LCP procedure of thefirst aspect, introduces a second prioritization level based on theProSe LCG priorities. Accordingly, in a first prioritization accordingto the first aspect, the UE selects that ProSe destination group havingthe highest priority, such that the generated PDU will only containProSe data to be transmitted to UEs of said selected ProSe destinationgroup. Then, in a second prioritization, the available resources areallocated to the ProSe logical channels of said selected ProSedestination group by taking into account the ProSe LCG priorityassociated to the ProSe LCGs to which the ProSe logical channels aremapped, i.e. the ProSe logical channels are served in a decreasing orderof their corresponding ProSe LCG priority. The PDU is thus sequentiallyconstructed with ProSe data of the one selected ProSe destination groupand from ProSe logical channels in a decreasing ProSe LCG priority orderassociated therewith. The thus generated PDU is then further processedand transmitted.

One of the advantages achieved by the LCP procedure of the secondaspect, in addition to the advantage of the first aspect, is that ProSedata associated with delay-critical services (such as Voice over IP) isnot delayed unnecessarily, since the corresponding ProSe logicalchannels carrying said delay-critical data are served according to theirassociated priority (associated via the mapped ProSe LCG).

Variants of the second aspect differ as to how the mapping of the ProSelogical channels to the ProSe LCGs is performed. For example, in onevariant, a plurality of ProSe LCGs is defined, irrespective of any ProSedestination groups, and each of the ProSe logical channels configured inthe user equipment is mapped to one out of the plurality of the ProSeLCGs, i.e. irrespective of the association between ProSe logicalchannels and ProSe destination groups. For instance, four different LCGsin total can be pre-defined for ProSe, and the UE, when or after settingup the ProSe logical channels, maps each of the ProSe logical channelsto one of the four ProSe LCGs. In this variant, the four ProSe LCGs canbe unambiguously identified by the corresponding LCG-ID. In analternative variant, for each ProSe destination group a different set ofdifferent ProSe LCGs is defined, e.g. the plurality of ProSe LCGs forone ProSe destination group is different from the ProSe LCGs from anyother ProSe destination group. For instance, when assuming fourdifferent LCGs per ProSe destination group, and 8 different ProSedestination groups, effectively there would be 8×4=32 different ProSeLCGs, identifiable e.g. by a combination of the ProSe destination groupID and the ProSe LCG-ID. Then, for each of the ProSe destination groups,each of the ProSe logical channels associated with said ProSedestination group is mapped to one of the ProSe LCGs of the ProSedestination group. For the latter variant, prioritization can be definedand implemented more precisely.

According to further variants of the second aspect, the buffer statusreporting procedure for ProSe is adapted to the improved LCP procedureso as to include more buffer size information and thus allowing the eNB,receiving said ProSe BSR, to schedule ProSe resources more efficiently.In particular, a ProSe buffer status report is generated to include foreach pair of ProSe destination group and ProSe LCG (e.g. actively usedin the UE, and/or e.g. for which ProSe data is available), buffer sizeinformation of the available ProSe data for those ProSe logical channelsbeing associated with the ProSe destination group and ProSe LCG of thepair. The UE then transmits the generated ProSe buffer status report toa radio base station controlling the radio resources for the userequipment in the mobile communication system.

According to a third aspect of the present disclosure, the ProSedestination group is additionally used to select an appropriate resourcepool for the UE-autonomous resource scheduling mode (Mode 2). Inparticular, a plurality of radio resource pools are configured for theuser equipment, e.g. by the eNodeB and/or a responsible ProSefunction/entity in the network. As explained already for the firstaspect, the ProSe destination groups are served in a decreasing order ofpriority with respect to the available radio resources.

Then, after this step of selecting the ProSe destination group, the UEselects one of said resource pools based on the selected ProSedestination group. This can be done in different ways.

In one variant, there is an association between each ProSe destinationgroup and one of said resource pools, which can be determined centrallyby a responsible ProSe function/entity in the network and is thentransmitted to the UE or which is preconfigured in the UE.Correspondingly, the UE can then select that radio resource pool whichis assigned to the selected ProSe destination group.

In an alternative variant, each of the radio resource pools is assigneda particular priority (e.g. by the ProSe function/entity mentionedbefore); the UE is also informed about the priority of each radioresource pool, e.g. in system information broadcast by a radio basestation in its cell. After the ProSe destination group is selectedaccording to the first step, the priority of said selected ProSedestination group is compared by the UE with the priorities of theavailable radio resource pools so as to select one particular radioresource pool. For example, an appropriate radio resource pool wouldhave the same (or a lower) priority than the priority of the selectedProSe destination group, such that only ProSe data of ProSe logicalchannels belonging to a ProSe destination group with a group priority ofthe same (or higher) than the priority associated to the resource poolare transmitted with resources of said corresponding resource pool.

Correspondingly, in one general aspect, the techniques disclosed herefeature a method for allocating radio resources to logical channels whenperforming a logical channel prioritization, LCP, procedure in a userequipment of a mobile communication system. A plurality of logicalchannels for Proximity Services, ProSe, are configured in the userequipment and are associated with one out of a plurality of ProSedestination groups as possible destinations of ProSe data. Furthermore,each of the plurality of ProSe destination groups is associated with aProSe destination group priority, and each of the plurality of ProSelogical channels is mapped to one out of a plurality of ProSe LogicalChannel Groups, LCGs. Also, each of the plurality of ProSe LCGs isassociated with a ProSe LCG priority. The user equipment performs thefollowing steps when generating a first Protocol Data Unit, PDU, fortransmission. The UE selects that ProSe destination group with ProSedata available for transmission with the highest ProSe destination grouppriority. Then, the UE allocates radio resources to those ProSe logicalchannels with ProSe data available for transmission, that are associatedwith the selected ProSe destination group, in a decreasing order of theProSe LCG priority associated with the ProSe LCGs to which those ProSelogical channels are mapped.

According to an advantageous variant which can be used in addition oralternatively to the above, the ProSe LCG priority is eitherpre-configured in the user equipment, or determined by a ProSe functionin a ProSe entity of the mobile communication system and communicated tothe user equipment. In the latter case, the determined ProSe LCGpriority is optionally also communicated to a radio base stationcontrolling the radio resources for the user equipment in the mobilecommunication system.

According to an advantageous variant which can be used in addition oralternatively to the above, the ProSe destination group priority iseither pre-configured in the user equipment, or determined in a ProSefunction in a ProSe entity of the mobile communication system andcommunicated to the user equipment. In the latter case, the determinedProSe destination group priority is optionally also to a radio basestation controlling the radio resources for the user equipment in themobile communication system.

According to an advantageous variant which can be used in addition oralternatively to the above, the mapping of the ProSe logical channels tothe ProSe LCGs is performed by defining a set of different ProSe LCGs,wherein each of the ProSe logical channels configured in the userequipment is mapped to one out of the set of plurality of differentProSe LCGs; for example, the different ProSe LCGs are identified by aProSe LCG ID. Alternatively, for each ProSe destination group adifferent set of different ProSe LCGs is defined, and each of the ProSelogical channels associated with one out of the plurality of ProSedestination groups is mapped to one of that set of different ProSe LCGsdefined for said one of the plurality of ProSe destination groups; forexample, the different ProSe LCGs are identified by a combination of anID for the ProSe destination group and an ID for the ProSe LCG.

According to an advantageous variant which can be used in addition oralternatively to the above, a ProSe buffer status report is generated bythe user equipment, including for each pair of ProSe destination groupand ProSe LCG, buffer size information of the available ProSe data forthose ProSe logical channels being associated with the ProSe destinationgroup and ProSe LCG of the pair. Then, the generated ProSe buffer statusreport is transmitted to a radio base station controlling the radioresources for the user equipment in the mobile communication system. Inone example, the ProSe buffer status report includes the followinginformation for each pair of ProSe destination group and ProSe LCG: theProSe destination group identity of the ProSe destination group of thepair, a ProSe LCG identity of the ProSe LCG of the pair, and buffer sizeinformation of the available ProSe data for those ProSe logical channelsbeing associated with the ProSe destination group and ProSe LCG of thepair.

According to an advantageous variant which can be used in addition oralternatively to the above, a scenario is assumed where ProSe data forthe ProSe destination group with the highest priority is still availablefor transmission after generating the first PDU, and ProSe data isavailable to be transmitted to at least another ProSe destination group.In said case, when generating a second PDU for transmission, the userequipment either selects that ProSe destination group with ProSe dataavailable for transmission with the highest ProSe destination grouppriority, or selects that ProSe destination group with ProSe dataavailable for transmission with the second-highest ProSe destinationgroup priority.

According to an advantageous variant which can be used in addition oralternatively to the above, two sets of radio resources are available tothe user equipment, wherein a first of the two sets of radio resourcesis used for the allocation of radio resources for the first PDU, and asecond of the two sets of radio resources is used for the allocation ofradio resources for the second PDU.

Correspondingly, in one general aspect, the techniques disclosed herefeature a method for allocating radio resources to logical channels whenperforming a logical channel prioritization, LCP, procedure in a userequipment of a mobile communication system. A plurality of logicalchannels for Proximity Services, ProSe, are configured in the userequipment and are associated with one out of a plurality of ProSedestination groups as possible destinations of ProSe data. Furthermore,a plurality of radio resource pools are configured for the userequipment, and each of the plurality of ProSe destination groups isassociated with a ProSe destination group priority. The user equipmentperforms the following steps when generating a first Protocol Data Unit,PDU, for transmission. The UE selects that ProSe destination group withProSe data available for transmission with the highest ProSe destinationgroup priority. Then, the UE selects the radio resource pool based onthe selected ProSe destination group. Then, the UE allocates allocatingradio resources of the selected radio resource pool to those ProSelogical channels with ProSe data available for transmission, that areassociated with the selected ProSe destination group.

According to an advantageous variant which can be used in addition oralternatively to the above, the step of selecting the radio resourcepool based on the selected ProSe destination group can be performedeither by the user equipment according to association information,received from a network entity or pre-configured in the user equipment,indicating for each of the plurality of ProSe destination groups anassociated radio resource pool out of the plurality of radio resourcepools. Or, when each of the radio resource pools is assigned one out ofa plurality of pool priorities, the user equipment selects that radioresource pool with an appropriate pool priority compared to the ProSedestination group priority of the selected ProSe destination group. Inone example, the UE shall select the radio resource pool that has a poolpriority that is the same or lower than the ProSe destination grouppriority of the selected ProSe destination group. In one furtherspecific example, the user equipment is informed about the pool priorityof each radio resource pool via broadcast information transmitted from aradio base station controlling the radio resources for the userequipment in the mobile communication system.

According to an advantageous variant which can be used in addition oralternatively to the above, each of the plurality of ProSe logicalchannels is mapped to one out of a plurality of ProSe Logical ChannelGroups, LCGs. Further, each of the plurality of ProSe LCGs is associatedwith a ProSe LCG priority, and the step of allocating allocates theradio resources of the selected radio resource pool to those ProSelogical channels with ProSe data available for transmission, that areassociated with the selected ProSe destination group, in a decreasingorder of the ProSe LCG priority associated with the ProSe LCGs to whichthose ProSe logical channels are mapped. Correspondingly, in one generalaspect, the techniques disclosed here feature a user terminal forallocating radio resources to logical channels when performing a logicalchannel prioritization, LCP, procedure in the user equipment of a mobilecommunication system. A plurality of logical channels for ProximityServices, ProSe, are configured in the user equipment and are associatedwith one out of a plurality of ProSe destination groups as possibledestinations of ProSe data. Each of the plurality of ProSe destinationgroups is associated with a ProSe destination group priority, whereineach of the plurality of ProSe logical channels is mapped to one out ofa plurality of ProSe Logical Channel Groups, LCGs, and wherein each ofthe plurality of ProSe LCGs is associated with a ProSe LCG priority. Aprocessor of the UE selects that ProSe destination group with ProSe dataavailable for transmission with the highest ProSe destination grouppriority, when generating a first Protocol Data Unit, PDU, fortransmission. The processor furthermore allocates radio resources tothose ProSe logical channels with ProSe data available for transmission,that are associated with the selected ProSe destination group, in adecreasing order of the ProSe LCG priority associated with the ProSeLCGs to which those ProSe logical channels are mapped.

According to an advantageous variant which can be used in addition oralternatively to the above, a storage medium of the UE stores the ProSeLCG priority being pre-configured in the user equipment. Alternativelyor in addition, a receiver of the UE receives from a ProSe function in aProSe entity of the mobile communication system the ProSe LCG priority,determined by said ProSe function. Also possible, the storage medium ofthe UE stores the ProSe destination group priority being pre-configuredin the user equipment, and/or the receiver receives from a ProSefunction in a ProSe entity of the mobile communication system the ProSedestination group priority determined by said ProSe function. Accordingto an advantageous variant which can be used in addition oralternatively to the above, the processor maps each of the ProSe logicalchannels configured in the user equipment to one out of a set ofdifferent ProSe LCGs. Alternatively, for each ProSe destination group adifferent set of different ProSe LCGs is defined, and the processor mapseach of the ProSe logical channels associated with one out of theplurality of ProSe destination groups to one of that set of differentProSe LCGs defined for said one ProSe destination group.

According to an advantageous variant which can be used in addition oralternatively to the above, the processor generates a ProSe bufferstatus report, including for each pair of ProSe destination group andProSe LCG, buffer size information of the available ProSe data for thoseProSe logical channels being associated with the ProSe destination groupand ProSe LCG of the pair. The transmitter of the UE then transmits thegenerated ProSe buffer status report to a radio base station controllingthe radio resources for the user equipment. In one example, the ProSebuffer status report includes the following information for each pair ofProSe destination group and ProSe LCG: the ProSe destination groupidentity of the ProSe destination group of the pair, a ProSe LCGidentity of the ProSe LCG of the pair, and buffer size information ofthe available ProSe data for those ProSe logical channels beingassociated with the ProSe destination group and ProSe LCG of the pair.

According to an advantageous variant which can be used in addition oralternatively to the above, it is assumed that ProSe data for the ProSedestination group with the highest priority is still available fortransmission after generating the first PDU, and ProSe data is availableto be transmitted to at least another ProSe destination group. Then, theprocessor still selects that ProSe destination group with ProSe dataavailable for transmission with the highest ProSe destination grouppriority, when generating a second PDU for transmission. Alternatively,the processor selects that ProSe destination group with ProSe dataavailable for transmission with the second-highest ProSe destinationgroup priority, when generating a second PDU for transmission.

Correspondingly, in one general aspect, the techniques disclosed herefeature a user terminal for allocating radio resources to logicalchannels when performing a logical channel prioritization, LCP,procedure in the user equipment of a mobile communication system. Aplurality of logical channels for Proximity Services, ProSe, areconfigured in the user equipment and are associated with one out of aplurality of ProSe destination groups as possible destinations of ProSedata. A plurality of radio resource pools are configured for the userequipment, wherein each of the plurality of ProSe destination groups isassociated with a ProSe destination group priority. A processor of theUE selects that ProSe destination group with ProSe data available fortransmission with the highest ProSe destination group priority, whengenerating a first Protocol Data Unit, PDU, for transmission. Theprocessor then further selects the radio resource pool based on theselected ProSe destination group. Finally, the processor allocates radioresources of the selected radio resource pool to those ProSe logicalchannels with ProSe data available for transmission, that are associatedwith the selected ProSe destination group. According to an advantageousvariant which can be used in addition or alternatively to the above, theprocessor selects the radio resource pool according to associationinformation, received from a network entity or being pre-configured inthe user equipment, indicating for each of the plurality of ProSedestination groups an associated radio resource pool. Alternatively, theprocessor selects that radio resource pool with an appropriate poolpriority compared to the ProSe destination group priority of theselected ProSe destination group, wherein each of the radio resourcepools is assigned one out of a plurality of pool priorities. Forexample, the processor selects that radio resource pool having a poolpriority that is the same or lower than the ProSe destination grouppriority of the selected ProSe destination group.

According to an advantageous variant which can be used in addition oralternatively to the above, each of the plurality of ProSe logicalchannels is mapped to one out of a plurality of ProSe Logical ChannelGroups, LCGs, and wherein each of the plurality of ProSe LCGs isassociated with a ProSe LCG priority. Then, the processor allocates theradio resources of the selected radio resource pool to those ProSelogical channels with ProSe data available for transmission, that areassociated with the selected ProSe destination group, in a decreasingorder of the ProSe LCG priority associated with the ProSe LCGS to whichthose ProSe logical channels are mapped.

Fifth Embodiment Advantageous for MCPTT

The MCPTT Service, as exemplified in the background section, shouldprovide a mechanism to prioritize MCPTT Group Calls based on thepriorities associated with elements of the call (e.g., service type,requesting identity, and target identity). This requirement implies thatthe priority of a group call can depend on the requesting identity (AKAthe user/UE originating the transmission), in addition to thecommunication target. This also confirms that the ProSe Layer 2 Group IDdoes not itself dictate priority. Rather the priority is worked outbased on a number of factors at the application layer of MCPTT.

While the above described embodiments may also be employed for LCP, thepresent, fifth embodiment, provides particular benefits for MCPTTservice. In particular, the group priority scheme introduced above mayhave some limitations and inflexibilities with respect to MCPTT. Forexample, let us consider a UE that participates in two ProSe Groupswhere group A communication is typically higher priority than group Bcommunication. Due to the destination group prioritization scheme whichfirst selects the group according to the group priority as describedabove, it would not be possible to support an emergency situation withingroup B where it would be desirable to priorities this specific group Btraffic over all other traffic.

In the following description, the examples are described on the basis ofthe MCPTT service studies by the 3GPP currently. However, it is notedthat this mechanism is employable for any kind of ProSe system in whichpriorities of different services and destinations are of importance forefficient group call operation.

It is the particular solution provided by embodiment 5, that eachsidelink logical channel is assigned a priority level. The UE performslogical channel prioritization (i.e. deciding the order to serve thedata queued on different SLRBs) based only on this priority levelwithout taking into account the destination group priority.

In fact, this 5th embodiment may also be implemented in a system notsupporting group priorities and merely assigning priority levels toparticular logical channels.

In particular, the UE performs the following steps as is illustrated inFIG. 25 . The UE selects in step 2510 the highest priority sidelinklogical channel (having data available). The highest priority LC here isthe LC having the highest priority among all LCs of all destinationgroups attended to by the UE. The selected sidelink logical channeldetermines the ProSe destination group. Thus, the UE determines in step2520 the destination group to which the highest priority logical channelbelongs. The determined destination group is then selected for datatransmission and further prioritization is performed for the UE'slogical channels of the selected destination group. Accordingly, in step2530, the UE performs for all sidelink logical channels belonging to theselected ProSe destination group further prioritization. Then in step2540, all sidelink logical channels belonging to the determined ProSedestination group are served in decreasing priority order (based on thepriority associated to the respective sidelink logical channels of thedestination group). Being served means that the data from the respectivelogical channels are mapped onto the allocated resources in the currenttransmission instant (transmission opportunity, such as the abovedescribed sidelink control, SC, period).

The present procedure may be employed by the UE working in either mode 1(eNB controlled resource allocation mode) or in mode 2 (autonomousresource allocation mode). The present procedure may also operate inother systems, in which the transmission is controlled by another entitythan eNB. This is because it already assumes some resources beingavailable, irrespectively of the resource assignment procedure.

The above procedure is advantageously performed by the UE at everytransmission opportunity where a new transport block needs to begenerated. In the context of ProSe, the UE can according to the currentspecified ProSe functionality (Rel-12) only transmit data to one ProSegroup within the SC period. In that sense the UE only needs to selectthe ProSe destination group based on the sidelink logical channelpriorities once per SC period.

Still the step of the prioritization mechanism, i.e. the allocation ofradio resources to the sidelink logical channels belonging to theselected ProSe destination group according to their priority is to beperformed for each new transport block.

This provides the advantage that at forming of each new transport block,the UE which is allowed to transmit data uses the allocated capacity forconveying the most important data first. With each transport blocktransmission, the data available for transmission may change, and thusalso the selection of the destination group and the logical channelsaccording to the priorities may have different result from transportblock to transport block. Especially for critical data, fast possibilityof data transmission is important.

However, it is noted that the present disclosure is not limited to thisexample. For some applications it may be acceptable if the destinationgroup is selected and the scheduling is performed every K (integerlarger than 2) transport blocks. The remaining transport blocks areformed using the last allocation (thus transmitting to the last selecteddestination group and allocating resources to the logical channels forthe selected group according to their priorities.

The above described procedure merely assumes that there is a priorityfor each sidelink logical channel defined and available in the UE, forinstance temporarily or permanently stored. Moreover, there is alsoinformation available at the UE specifying for each sidelink logicalchannel, to which destination group it belongs.

For instance, the priority associated with each sidelink logical channelmay be determined either by the UE or by the ProSe function and signaledto UE and/or to the eNB.

In the case when the ProSe function determines the logical channelpriority, some signaling needs to be introduced between the ProSe entity(ProSe function) and the UE (and possibly the eNB).

For instance, the signaling may be a control signaling on a higherlayer, i.e. a layer beyond the physical layer and the MAC layer. Inparticular, a protocol message may include a logical channel priorityfor each logical channel. The logical channel priority may be configuredby the ProSe entity when establishing the sidelink logical channel atthe UE, for instance in accordance with at least one of the UE identity,the destination group identity of the LC, the logical channel group towhich the LC belongs, and/or the particular service carried by the LC orthe like. The priority associated to a sidelink logical channel can bealso changed or reconfigured when triggered for example by theapplication layer.

In general, a priority level could be also associated to each datapacket of a service (such as application layer packets). Packets of thesame priority level are mapped to the same bearer, i.e. sidelink logicalchannel. For example, if a ProSe service generates data packets whichare associated with two different priority levels (for instance, voiceand video in a video call may have different priorities), then the ProSefunction (in ProSe entity) may configure the UE to establish twosidelink logical channels for the respective two data flows of the ProSeservice, to which the packets are mapped to according to theirpriorities. In that sense, the prioritization procedure as describedabove can be also performed based on the priority levels associated todata packets of a service.

In mode 1, in which the resource assignment is controlled by the eNB,the eNB may be provided with the same configuration information as theUE. More in particular, the eNB may be provided with the priority levelsassociated to the respective established sidelink logical channels. Thepriority levels associated with the respective established sidelink LCsmay be provided to the eNB by the ProSe entity or by the UE.

Alternatively, the eNB could be provided with the mapping information ofsidelink logical channels to logical channel groups and thecorresponding priority level of the logical channel groups in accordancewith the sidelink logical channel priority. Based on the priorityinformation and the sidelink buffer status report, the eNB is able toperform an efficient scheduling considering the priorities oftransmissions from different UEs. According to the current definedsidelink buffer status report MAC control element, the UE reports thebuffer status per ProSe destination group-logical channel group pair.Therefore it is beneficial to provide the eNB information on thepriorities of the sidelink logical channels mapped to the correspondingProSe destination group, i.e. onto these LCG pairs.

Advantageously, within the signaling from the ProSe entity the UE and/oreNB is configured with a sidelink logical channel priority and withmapping of the sidelink logical channel to LCGs and the destinationgroups.

In the case when the UE determines the logical channel priority for asidelink logical channel on its own, it is assumed that the UE and/orthe eNB is configured with a ProSe destination group priority and theLCG priority. This may be performed by the ProSe function in the ProSeentity as described for the previous embodiments.

It is noted that irrespectively of whether the UE determined the logicalchannel priority on its own or receives the configuration from the ProSeentity, the eNB may still do either of calculating the priorities orreceive the configuration from the ProSe entity.

The UE (or possibly also eNB) then calculates based on some predefinedformula the logical channel priority. For instance, the sidelink logicalchannel priority may be calculated as a product of the ProSe grouppriority (SLRBi) and the LCG priority (SLRBi). In general:sidelink logical channel priority=f(SLRBi,SLRBi)with f being an arbitrary function which is preferably proportional tothe ProSe group priority (SLRBi) and the LCG priority (SLRBi). Thelogical channel priority may be calculated based on the destinationgroup priority and the LCG priority as described in the previousembodiments.

The calculation of the logical channel priority is illustrated in FIG.26 . The flow diagram of the method 2600 in FIG. 26 may be executed inany of the UE and the eNB. It may be used in mode 1 as well as in mode2. In step 2610, the UE and/or eNB determines the destination group ofthe logical channel for which it is calculating the priority. Thisdetermination may be performed in response to receiving controlinformation from the ProSe entity including the priority of thedestination group. In step 2620, the UE determines the LCG priority forthe logical channel for which it is calculating the priority. This mayalso be performed upon receiving the LGC priority from the ProSe entity.In step 2630, further parameters which may be used for determining thelogical channel priority may be determined such as the UE's geographiclocation, UE emergency status or ID or others. Finally, in step 2640,the calculation based on these parameters is performed. The aboveapproach 2600 may be performed by the UE and/or eNB for all logicalchannels configured for the UE.

Concerning the ProSe BSR reporting (Mode 1), the control elementsdefined in MAC of the ProSe Buffer status Reporting in the Rel-12 may bereused. In particular, in case sidelink LCs belonging to one ProSedestination group can be mapped to 4 different LCGs, the ProSe BSR canessentially distinguish between 64 different destination groups-LCGpairs (corresponding to 4-bit long destination group ID and 2-bit longLCG ID). Such signaling should provide enough granularity for anefficient scheduling to be performed by the eNB.

In Mode 2 (autonomous resource allocation mode), the resource poolselection as described above may be used. Based on selected ProSedestination group (which was selected based on sidelink logical channelwith the highest priority), the resource pool is selected. Essentiallythe resource pools, which are configured by the cell for the autonomousresource allocation mode, should be associated with any kind ofpriority, e.g. group priority or logical channel priority, in order thatthe UE selects from the relevant resource pools. This should providesufficient means to separate the resources used by UEs performing ProSetransmissions with different associated priorities. The eNB could forexample configure different physical parameters for resource pools ofdifferent priorities. From UE side, when a UE wants to perform a ProSetransmission in the autonomous resource allocation mode, it first needsto select a ProSe destination group based on associated priorities, e.g.according to the logical channel priority. Based on the selected ProSedestination group the UE shall select the Tx resource pool from the listof resource pools. More in particular UE shall use a Tx resource poolhaving an associated priority which is same or lower than the priorityof the selected ProSe destination group or alternative the priority ofthe highest priority logical channel (based on which the ProSedestination group was selected).

In other words, the UE advantageously further selects the resources tobe allocated for the transmission of the data from a resource pool andto select the resource pool among a plurality of resource poolsaccording to the destination group priority or a logical channelpriority associated with a logical channel from which the data is to betransmitted. It is beneficial if the logical channel priority accordingto which the resource pool is selected is the highest logical channelpriority among the logical channels for the destination group.

Alternatively, or in addition, there is a priority level associated toeach resource pool, which the UE compares with the highest prioritylogical channel within the selected ProSe destination group.

In order to provide a more situation responsive prioritizing for the PTTservice, which may be used for various emergency applications, thepriority of a sidelink logical channel might change based on the currentsituation, e.g. geographical position, emergency situation, firstresponder etc.

The change of the logical channel priority may be performed dynamically,which means that it does not have to remain the same during thegroupcall (for the bearer set up) but may change.

The modification may be performed by a reconfiguration of the logicalchannel parameter, i.e. priority. This may be performed by the AccessStratum which includes protocols below the Non-Access Stratum as definedin the background section.

Alternatively, a new logical channel is set up with the new modifiedpriority while the logical channel with the old priority is maintaineduntil the buffer is empty and then it is removed. Especially, in thecase when the new priority is higher than the old priority, thisapproach may be beneficial in order to treat the packets of this newlogical channel with higher priority. Optionally, the logical channelwith the current (old) priority may be closed (removed). The prioritymodification may be triggered by the ProSe entity on the applicationlayer.

If the UE reconfigures the priority for a logical channel, for whichstill transmission data is stored in the buffer, it may be generallybeneficial to maintain the old priority (priority before itsmodification) valid for the that data in the buffer. This is also thecase if the priority modification is lowering the priority. As the datain the buffer were generated while the logical channel had a higherpriority, maintaining the old priority ensures that these data areconveyed faster.

An alternative behavior upon modification of the logical channelpriority for a channel for which the buffer still contains data fortransmission is to immediately flush the buffer in order to make surethat the new data is treated first. This behavior may be beneficialespecially if the priority of the logical channel is modified to ahigher priority.

Accordingly, if the current priority is higher than the modifiedpriority, the UE may still transmit the data buffered before themodification with the current priority while treating the data bufferedafter the modification with the new priority. On the other hand, if thecurrent priority is lower than the new priority, the UE may remove fromthe buffer data stored before the modification, i.e. flush the buffer.

The buffer flushing may imply that the flushed data get lost. Especiallyfor conversational services as a (PTT) call or video call,retransmissions on higher layer such as application layer may not beuseful. However, the present disclosure is not limited thereto and theremay be some retransmission mechanism implemented in the higher layers.

However, it is noted that the rule to maintain the old priority for thebuffered data may also be applied upon modification irrespectively ofthe type of change (increasing or decreasing the priority). The presentdisclosure is generally not limited to a particular behavior uponpriority modification and the buffer may also be always flushed.

Further alternatives may be advantageous for certain scenarios. Forinstance, the UE behavior upon priority modification may depend on thereason of modification. For instance, if the logical channel prioritychanges due to emergency level change while the change is an increase,the buffer is flushed. Otherwise, the buffer is not flushed.

Alternatively, the buffer flushing may be controlled by the ProSefunction by including into the priority modification message a bufferflush flag which can take two values, one indicating that the buffer isto be flushed and the other one indicating that the data is to bemaintained.

Still alternatively, the UE behavior may depend on the priority valueafter modification. For instance, the buffer is flushed only if themodified priority is higher than a predefined threshold priority level.Accordingly, the most important data (for instance data with the highestpriority only) shall be transmitted the fastest possible, while the dataof other priorities would be handled with increased fairness.

Sixth Embodiment: Logical Channel Suspension

According to another embodiment of the present disclosure, afloor-control mechanism is provided. This embodiment may workindependently of the previous embodiments or may be combined with any ofthe embodiments previously described. This sixth embodiment may also beemployed with both Mode 1 and Mode 2.

The MCPTT service has several particularities. In particular, at onetime, only a single party (member of the group call) may transmit(broadcast) data/talk. Accordingly, a mechanism for selecting whichmember is to transmit may have a substantial impact on the systemefficiency. In the context of the push-to-talk systems, the term“floor-control” denotes the process of selecting which particular userin the group is allowed to talk and notifying the particular user,especially in the case when there are more users trying to transmit dataat the same transmission opportunity.

Based on the 3GPP SA6 TR 23.779, v0.6.0, “Study on System ArchitectureEnhancements for Mission Critical PTT over LTE”, available atwww.3gpp.org, some proposals have been made to use application layersignaling to support floor control, essentially by one UE requesting thefloor for a particular channel, and the applications in other UEsturning off their transmission on receiving such a request.

When the user equipment in the current studies does not have floor, andthus stops its transmission, the logical channels still remain activeand are also used by the terminal for prioritizing of the datatransmission to different groups.

In this embodiment, a user equipment operable in a wireless push to talkcommunications system supporting direct communication between a group ofuser equipments is provided. The user equipment includes a floor controlunit that determines whether the user equipment is selected to transmitdata among user equipments of the wireless communication system. If theuser equipment is not selected, suspend its sidelink logical channelsbelonging to the ProSe group (group of user equipments, i.e. destinationgroup from the point of view of one particular UE). If, on the otherhand, the data originating user equipment is selected, resume itssidelink logical channels which were previously suspended.

Advantageously, the suspended logical channels are not considered forprioritizing and resource allocation as described in the aboveembodiments.

The group of user equipment may be formed by two or more UEs. The floorcontrol unit may be implemented by a processor, possibly also the sameprocessor as the one which may be used by prioritizing procedure asdescribed in preceding embodiments.

The determination of whether the data equipment was selected, may beperformed in various different ways, depending on the implementation ofthe floor control. This embodiments may work with any such floorcontrol, irrespectively of the layer on which the floor control takesplace.

There is, for instance, one entity which is providing the group callmembers with allowance to transmit data. The central entity may be auser equipment, one of the members of the group call. For example, a UEtransmits a request for floor (floor request message) and the centralentity grants the request. The floor grant message may be broadcast sothat the remaining stations receive it and determine that they are notselected, i.e. not allowed to transmit. It is noted that this example isnot to limit the present disclosure. The central entity may also be adevice different from a UE. It may be, for instance an eNB or anotherentity such as a relay or a server.

Advantageously, the floor control (transmission of floor requestmessages and possibly floor grants) is performed on a higher layer, i.e.above MAC. In particular, the floor control may be performed on anapplication layer.

Alternatively, there may be no central entity involved. In particular,the UEs may all receive the floor request and stop their transmissionfor the given time. For example based on their own priority and thepriority of other UEs within the group requesting the “floor” each UEitself could decide whether to temporarily suspend sidelink logicalchannels or the ProSe group transmissions or to resume them, as will bealso described in more detail in the following embodiment.

The suspending and resuming may be performed in various different ways.When the logical channel is suspended, the buffer content is maintainedand the data stored therein are transmitted upon resuming the logicalchannel.

In summary, based on the result of the floor control mechanism, sidelinklogical channels or ProSe destination groups can be suspended and againresumed for the LCP procedure. The suspension and/or resuming mayadvantageously be performed (initiated) by a higher layer, such asapplication layer. In particular, according to an exemplaryimplementation, the higher layer will inform lower layers tosuspend/resume certain sidelink logical channels/ProSe groups.

According to one exemplary implementation each sidelink logical channelhas an associated status flag stored in the UE, which indicates whetherthe corresponding sidelink logical channel is suspended or “active”.Higher layer within the UE, e.g. ProSe function, sets the flag accordingto the result of the floor control mechanism running on the applicationlayer. The LCP procedure within the MAC considers during the transportblock generation procedure not only the priority of sidelink logicalchannel or any other priority like ProSe group priority and LCGpriority, but also the status of this flag, More in particular for thegeneration of a new transport block the LCP procedure or MAC layerconsiders only those sidelink logical channels for which the status flagis not set to suspended. When looking at FIG. 25 , this means that instep 2510 the LC with the highest priority is selected among those LCswhich have the active flag set (i.e. which are active rather thansuspended). The prioritization in step 2530 is also performed only amongactive channels.

In case a higher priority UE is transmitting currently, sidelinktransmission of other UEs within the group shall be suspended. LCPprocedure in the UE will not consider suspended sidelink logicalchannels/ProSe groups. As described above this will result in that theUE will not generate and transmit a new transport block with data of asuspended sidelink logical channel respectively ProSe group.

In case the floor control mechanism acknowledges/allows a sidelinktransmission for a UE within a ProSe group, the sidelink logicalchannels belonging to the ProSe group shall become active (resumed). TheLCP procedure in the UEs considers active/resumed sidelink logicalchannels/ProSe groups. Higher layer (application layer) maysuspend/resume sidelink logical channels/ProSe groups and inform MACabout it.

In particular, the UE may perform also the following: In case the higherlayer suspends a sidelink logical channel/ProSe group for which UE iscurrently transmitting data within an SC period, the UE shall stoptransmission of the SCI/data (DTX) within the SC period.

The UE will not consider the suspended sidelink logical channels/ProSegroups for the LCP/BSR/grant selection procedure for the next SC period.FIG. 27 illustrates an exemplary method 2700 according to the sixthembodiment. In particular, if the UE obtains the floor in a certainProSe group (which is evaluated in step 2710) then the UE considers allsidelink logical channels (if there are any suspended logical channelsbelonging to the ProSe group, resumes those logical channels) for theProSe group in step 2720 as resumed or active and transmits the data instep 2730 from the buffers of the logical channels according to theprioritizing and allocation procedure as described in embodiments 1 to5. If, on the other hand, the UE has not the floor, then in step 2740,it shall suspend all logical channels of the certain ProSe group.

Seventh Embodiment

In the above embodiment, the floor control was described as a meremechanism for assigning the floor to the UEs which request it withoutevaluating their needs. However, especially in the mission criticalscenario, floor control may be more efficient if the floor is givenfirst to the UEs which have more critical need to communicate theirdata.

Basically, an efficient floor control requires the ability of one UE topreempt another in order to enable a fair usage of themulticast/broadcast resources by a plurality of users (two or more).

The floor control thus also requires rules for assigning the channel todifferent users. Accordingly, prioritizing of the users rather thanmerely cyclically scheduling users that have data to be transmitted isalso of benefit.

In this embodiment, the floor control is based on a priority of a ProSeuser, which will be called a UE priority in the following. This prioritymay in general be a priority independent of the logical channelpriority, logical channel group priority or the group priority asdescribed above. However, the UE priority may also be related to thepriority of a sidelink transmission of a ProSe user within a given ProSegroup. In other words, there may be a mapping between the logicalchannel priority, logical channel group priority and/or the destinationgroup priority and the UE priority.

The UE priority handling in floor control is schematically illustratedin FIG. 28 . In particular, the method 2800 includes the step ofextracting 2810, from a sidelink control information on physical layeror a medium access control, MAC, protocol data unit, PDU, received fromanother user equipment, a user equipment priority indicator, wherein theuser equipment priority indicator indicates the priority of the userequipment or the data to be transmitted by the user equipment. In step2820, the extracted user equipment priority indicator is compared withan own user equipment priority stored in the user equipment or apriority of the data to be transmitted. If the own user equipmentpriority is lower than the extracted user equipment priority, it isdetermined (for instance, corresponding to step 2710 described withrespect to FIG. 27 ) that the user equipment is not selected for thetransmission and the data buffered for the logical channels of the userterminal are not transmitted 2830.

It is noted that step 2830 may also include suspending the logicalchannels of the user equipment for the ProSe destination group asdescribed in the sixth embodiment.

If, on the other hand, the own user equipment priority is higher thanthe extracted user equipment priority of all other terminals requestingfloor, it is determined (for instance, corresponding to step 2710described with respect to FIG. 27 ) that the user equipment is selectedfor the transmission and the data buffered for the logical channels ofthe user terminal are transmitted 2840. The transmission 2840 may beperformed based on the prioritization mechanism as shown in any of theembodiments 1 to 5.

If two or more UEs which send the floor request have the same priority,highest among the UEs of the group, those UEs with same priority may alltransmit or some random selection may be performed by each UE to decidewhether to transmit or not. In general, this should happen very rarelyif at all for the MCPTT service.

Even though the intention indicated in the previous embodiment has beento apply the floor control on the application layer, the priority of asidelink transmission or a ProSe user is advantageously an input to thefloor control mechanism. Thus, it may be beneficial to move at least aportion of the floor control to lower layers, i.e. to the physical layeror MAC as exemplified above.

Accordingly, data or/and the related sidelink control information (SCI)includes some priority information, based on which the “floor control”mechanism can be realized on PHY/MAC layer, which has latency advantagescompared to some higher layer “floor control” mechanism. The SCIinformation is another name for the concept of the scheduling assignment(SA) described already above in the background portion for both Mode 1and Mode 2.

In particular, PHY and MAC layer protocol have a lower latency comparedto an application layer protocol. Thus, it is advantageous to addpriority indication to PHY/MAC signaling. For instance the sidelinkcontrol information may include a priority field 2900 as shown in FIG.29 . The SCI is a control message of physical layer which may beapproximately compared to DCI in the LTE, Rel. 8 and later. It basicallyincludes the allocation information as described above under the namescheduling assignment (SA), i.e. it may specify closer the resources,for example including any of modulation and coding, redundancy version,frequency band, (sub)frame, MIMO parameters or the like etc.

The UE which is transmitting to a certain ProSe group (destination groupID), compares its own priority, which may be signaled by higher layer(and may be set by the ProSe entity) or preconfigured in the terminal,or the priority of the data to be transmitted with the priority receivedwithin the priority field 2900 (user equipment priority, UEP) of SCIreceived from other UEs in the same group. If the priority in thereceived SCI message is higher than the own priority, the transmittingUE will stop transmitting data/SCI for this SC period and possibly alsoin subsequent SC periods.

In particular, the UE priority may be preconfigured by the manufactureror operator in the UE. A simple but efficient implementation may beachieved by preconfiguring some UEs as master UEs which can preemptother UEs configured with lower priority.

Another, more flexible approach may be to configure the UE priority bythe ProSe entity, which provides the advantage of changing the UEpriority for different missions or different scenarios.

Still further, the UE priority may be determined autonomously by the UEor configured by the ProSe entity based on mapping of the logicalchannel priority. For instance, logical channel with the highestpriority maps on the high UE priority, whereas all other LC prioritiesmap on the low UE priority (here it is exemplarily assumed that the UEpriority can only take 2 values, high and low which may be 0 and 1 or 1and 0 respectively). The UE priority may then be determined by mappingthe highest LC of the UE for the given group onto a UE priority value.The above example is not to limit the present disclosure. Rather, themapping may look differently. For instance, there may be more than onehighest LC priority values mapping on the high UE priority. Moreover,the UE priority may take more than two values. It is noted that the UEpriority may also directly be the logical channel priority.

The configurable UE priority (by ProSe entity or by the UE itself) hasthe advantage that the priority may be flexibly changed. A UE prioritymay also be stored/configured per destination (ProSe) group so that oneUE may have a different priority in different ProSe groups.

With this approach, even if the floor is taken by a UE, it is ensuredthat another UE with higher priority may preempt the transmitting UE andtake the floor. This results in the UEs with higher prioritytransmitting their data with smaller latency than the remaining UEs. Theremaining UEs must wait until the floor is available for their prioritylevel. Depending on the deployment scenario, it may be beneficial toincrease the priority of the UE or the priority of the corresponding LCsproportionally to the time period during which the data have been storedin the buffer for transmitting.

Alternatively, or in addition to the priority field within SCI PHYmessages, data transport blocks (TBs) may also contain a priority fieldin the respective MAC header as is illustrated in FIG. 30 .

Based on the priority indication carried in the priority field of theMAC header the UE may decide whether or not to transmit data to theProSe group as described above.

In particular, a MAC PDU includes a MAC header and a MAC payload.

As shown in FIG. 30 , the currently used MAC header structure may bereused for signaling the priority field. In particular, MAC headeradvantageously contains the UE priority indication within the “R”reserved bit in the MAC subheader. The “R” field in the MAC has beenleft for use in later standard versions and is thus suitable tointroduce the priority indication and still maintain backwardcompatibility to earlier releases. The MAC header is described in 3GPPTS 36.321, v12.5.0, Section 6.2.4.

The UE priority field may carry a preemption indicator, which merelyindicates whether the UE transmits emergency data or normal data. The UEtransmitting the emergency data would then be able to preempt UEstransmitting normal data as exemplified above. In particular, thepriority indication may be a single bit of which one value indicates“emergency” whereas the remaining second value indicates normalpriority.

Since there is also a SRC (source) field in the MAC header whichidentifies the transmitting ProSe UE ID, the ProSe function (in theProSe entity) may provide a mapping between ProSe UE ID and thecorresponding UE priority which would basically indicate the basic UEpriority, i.e. the priority of the UE irrespectively of the particulardata currently transmitted. Together with the “R” field which could beused as described above as a kind of “emergency indicator” the receivingUE can calculate the priority of the transmitting UE and act thenaccording to the above described procedure, i.e. if the prioritydetermined by MAC header fields (in view of the basic UE priorityconfigured by the ProSe entity and stored in the own UE) is higher thanthe own priority, the UE will stop transmitting data in this SC periodand optimally in subsequent SC periods, i.e. number of subsequent SCperiods for which the UE is not transmitting data this ProSe group couldbe signaled or preconfigured. In other words, the UE may storeassignment between the UEs in the group and their basic priorities andto extract the UE priority indicator from the MAC header and tocalculate the current UE priority of a UEs in the group as a function ofthe basic priority and the extracted priority indicator. This may be,for instance a sum function or a multiplication or any other function.In this way, some UEs may be configured with higher priority (masters)whereas there still is also a possibility of UEs with lower priority topreempt the master UEs in the current case of emergency, i.e. if theemergency data are to be transmitted.

FIG. 31 illustrates an exemplary floor control mechanism. There is agroup G1 of three UEs, UE1 with floor control priority (UE priority) p=0corresponding to low priority, UE2 with a high priority p=1 and a UE3with the low priority p=0. Both, UE1 and UE2 submit SCI (SA) since theyhave data to be transmitted in a buffer for this group G1. Thecorresponding SA1 and SA2 are received by all respective terminals (orat least by UE1 and U2). UE1 extracts from the SA2 received from the UE2the priority p=1 of UE2 and compares it with the own priority p=0, whichis lower. Consequently, UE1 shall not transmit the data in the presentSC period. The UE2 received SA1 and makes similar comparison of theextracted p=0 with its own p=1 which is higher. Consequently, UE2 takesthe floor and transmits data, for instance speech data.

It is noted that the UE may advantageously stop transmission for longerthan the SC period. This may be advantageous especially for speech data,for which it is assumed that the speech portion will take several SCperiods to be transmitted. Thus, the UE may stop for the duration of afloor control period, larger than the SC period. The floor controlperiod may be configurable.

It is noted that this seventh embodiment may be advantageously combinedwith the sixth embodiment concerning suspending/resuming logicalchannels depending on the floor control results. However, the seventhembodiment may also work without the sixth embodiment. Similarly, theseventh embodiment may be advantageously combined with the first tofifth embodiment.

An example of a combination of the above embodiments is illustrated inFIG. 32 . In particular, group G1 similar to the example described withreference to FIG. 31 includes UE1, UE2, and UE3. All three UEs have datato be transmitted and thus, perform on their own the prioritizationprocedure as described in any of embodiments 1 to 5. As a result, UE1and UE2 are to transmit to group G1, whereas UE3 is to transmit toanother group. The transmission of SA1 and SA2 and their mutualreception by UE1 and UE2 is performed as described above. UE1 stops thetransmission and suspends its logical channels for group G1 according toembodiment 6.

In summary, as also illustrated in FIG. 33 , according to the fifthembodiment, a user equipment operable in a wireless communicationssystem supporting direct communication between user equipments,including: a storage 3320 with a sidelink configuration stored andspecifying a plurality of destination groups, each destination groupincluding possible destinations for sidelink data as well as storing alogical channel priority for each logical channel out of logicalchannels configured for the sidelink destination groups; a schedulingunit 3310 that: selects a sidelink destination group with a sidelinklogical channel having sidelink data available for transmission with thehighest logical channel priority among the sidelink logical channelshaving data available for transmission; and allocates radio resources tothe sidelink logical channels belonging to the selected sidelinkdestination group in decreasing priority order.

The user terminal may further include a transmission unit 3370 whichtransmits the data according to the prioritization performed and in theallocated resources.

Advantageously, the logical channel priority depends on at least two of:a destination group priority associated with a destination group thedata destination, a logical channel group priority associated with agroup of logical channels, grouped according to the type of datacarried, a geographical location of the user equipment, an emergencylevel in which the user equipment is operating, and a user equipmentidentifier.

The user equipment may further include a receiving unit 3360 forreceiving an indication of the logical channel priorities for therespective logical channels determined by a ProSe function in a ProSeentity of the mobile communication system and storing the logicalpriorities in the storage.

Alternatively, the scheduling unit 3310 of the user equipment determinesa logical channel priority for a logical channel at its end. This may beperformed on the basis of parameters received from the ProSe entity suchas group priority and/or LCG priority as well as based on furtherreceived and/or stored parameters.

The user equipment may further include a buffer 3330 for storing data tobe transmitted for a logical channel; and a priority setting unit 3340for modifying a current priority for said logical channel into amodified priority either based on own recalculation of the priority orbased on a command received from a ProSe function. As described above,the modification may be performed by opening a new logical channel withthe modified priority and let the logical channel with the remainingdata set up until the data in the buffer are transmitted.

Alternatively, the data stored in the buffer before modification areeither flushed or transmitted with the current priority depending on atleast one of: whether the current priority ID higher than the modifiedpriority; the level of the modified priority; and the cause ofmodification. Moreover, the user equipment may include a floor controlunit 3350 that determines whether the user equipment is selected totransmit data among user equipments of the wireless communicationsystem; if the user equipment is not selected, suspends its sidelinklogical channels; and, if the data originating user equipment isselected, resumes its sidelink logical channels which were previouslysuspended, wherein the scheduling unit does not consider the suspendedlogical channels for selecting and allocating resources to.

For example, the floor control unit 3350 may determine whether or notthe user equipment is to transmit data according to messages exchangedin the wireless communication system between the user equipments and/ora proximity service entity in a layer above MAC; and upon determiningthat the user equipment is not to transmit data, the user equipmentstops transmission of own data and/or sidelink control informationwithin a sidelink control period which is the period corresponding toone transmission of scheduling assignments and the corresponding data.

The floor control unit 3350 may also: extract, from a sidelink controlinformation on physical layer or a medium access control, MAC, protocoldata unit, PDU, received from another user equipment, a user equipmentpriority indicator, wherein the user equipment priority indicatorindicates the priority of the user equipment or the data to betransmitted by the user equipment; compare the extracted user equipmentpriority indicator with an own user equipment priority stored in theuser equipment or a priority of the data to be transmitted; if the ownuser equipment priority is lower than the extracted user equipmentpriority, determine that the user equipment is not selected for thetransmission.

In particular, if the user equipment has the floor and receives at thesame time sidelink control information from another user equipment witha higher user equipment priority, the floor control unit stops thetransmission and thus leaves the floor to the other user equipment.

The user equipment priority may be carried within a MAC header of theMAC PDU and be configured by a proximity services, ProSe, entity of thewireless communication system.

The user equipment may further include a buffer status reporting unitfor reporting to a network node of the wireless communication system thestatus of a buffer 3330 associated with the logical channel priority.

Furthermore, a network node operable in a wireless communications systemsupporting direct communication between user equipments is provided, thenetwork node including: a storage with a sidelink configuration storedper user equipment and specifying a plurality of destination groups,each destination group including possible destinations for sidelink dataas well as storing a logical channel priority for each logical channelout of logical channels configured for the sidelink destination groups;and a scheduling unit that: selects a sidelink destination group with asidelink logical channel having sidelink data available for transmissionwith the highest logical channel priority among the sidelink logicalchannels having data available for transmission; and allocates radioresources to the user equipment in the selected sidelink destinationgroup accordingly.

Moreover, the network node may further include a transmission unit fortransmitting a scheduling assignment to the user equipment for which thepriority determination and resource allocation has been performed. Thescheduling assignment is generated by the network node based on itsevaluation of priorities and resource requests from a plurality of UEsbelonging to one or more groups of UEs. The network node may be a basestation such as the eNB in the LTE or any other access point.

Moreover, a method is provided to be performed at a user equipmentoperable in a wireless communications system supporting directcommunication between user equipments, the method including: storing asidelink configuration specifying a plurality of destination groups,each destination group including possible destinations for sidelink dataas well as storing a logical channel priority for each logical channelout of logical channels configured for the sidelink destination groups;and selecting a sidelink destination group with a sidelink logicalchannel having sidelink data available for transmission with the highestlogical channel priority among the sidelink logical channels having dataavailable for transmission, and allocating radio resources to thesidelink logical channels belonging to the selected sidelink destinationgroup in decreasing priority order. Hardware and Software Implementationof the present disclosure

According to a first aspect, the invention improves the logical channelprioritization, LCP, procedure by which a user equipment allocates theavailable radio resources (e.g. allocated by a grant of the eNB orselected by the UE itself from a resource pool) to the different logicalchannels with available ProSe data. To said end, a prioritizationmechanism is introduced for the LCP procedure for managing the resourceallocation between the different ProSe logical channels. Although theprioritization mechanism is mostly described as if it were part of theLCP procedure, this is not necessarily the case, and it may bealternatively considered to be external to the LCP procedure.

As discussed in the background section, different ProSe destinationgroups are defined. According to the first aspect, each of the pluralityof ProSe destination groups is assigned one out of a plurality ofdifferent priorities, exemplarily termed ProSe destination grouppriority. The different ProSe destination groups are set up and managedby a corresponding ProSe function/entity in the network. According toone variant, the different ProSe destination group priorities can belikewise set up and managed in the network by said or another ProSeentity. In said case, information on the available ProSe destinationgroups and their corresponding priority levels shall be transmitted tothe UE. On the other hand, this information on the ProSe destinationgroups and their corresponding priority levels can also be transmittedto the eNB so as to allow the Enb to improve its scheduling of radioresources for said user equipment. According to still another variant,the ProSe destination groups and also their ProSe destination grouppriority can be pre-configured in the UE (and the radio base station),such that the exchange of information over the network is not necessary.

As mentioned before, different ProSe logical channels are set up in theuser equipment for ProSe direct communication, and are additionally alsoassociated with one out of the plurality of ProSe destination groups.When ProSe data is to be transmitted, i.e. ProSe data becomes availablefor transmission for the ProSe logical channel(s), the UE can performProSe direct communication in either eNB-scheduled Resource allocationmode (also referred to as Mode 1) or UE autonomous resource selectionmode (also referred to as Mode 2) depending on its configuration. Ineither way, the UE needs to allocate the available radio resources forProSe transmission (be it eNB-scheduled resources, or resources from aresource pool) between the different ProSe logical channels (e.g. STCHs)by performing an LCP procedure.

The improved LCP procedure of the first aspect considers the priority ofthe ProSe logical channels. In particular, a user equipment is provided,operable in a wireless communications system supporting directcommunication between user equipments, comprising: a storage with asidelink configuration stored and specifying a plurality of destinationgroups, each destination group including possible destinations forsidelink data as well as storing a logical channel priority for eachlogical channel out of logical channels configured for the sidelinkdestination groups; a scheduling unit configured to: select a sidelinkdestination group with a sidelink logical channel having sidelink dataavailable for transmission with the highest logical channel priorityamong the sidelink logical channels having data available fortransmission, allocate radio resources to the sidelink logical channelsbelonging to the selected sidelink destination group in decreasingpriority order.

Furthermore, a network node operable in a wireless communications systemsupporting direct communication between user equipments is provided, thenetwork node comprising: a storage with a sidelink configuration storedper user equipment and specifying a plurality of destination groups,each destination group including possible destinations for sidelink dataas well as storing a logical channel priority for each logical channelout of logical channels configured for the sidelink destination groups;and a scheduling unit configured to: select a sidelink destination groupwith a sidelink logical channel having sidelink data available fortransmission with the highest logical channel priority among thesidelink logical channels having data available for transmission,allocate radio resources to the user equipment in the selected sidelinkdestination group accordingly.

Moreover, a method is provided to be performed at a user equipmentoperable in a wireless communications system supporting directcommunication between user equipments, the method comprising: storing asidelink configuration specifying a plurality of destination groups,each destination group including possible destinations for sidelink dataas well as storing a logical channel priority for each logical channelout of logical channels configured for the sidelink destination groups;and selecting a sidelink destination group with a sidelink logicalchannel having sidelink data available for transmission with the highestlogical channel priority among the sidelink logical channels having dataavailable for transmission, and allocating radio resources to thesidelink logical channels belonging to the selected sidelink destinationgroup in decreasing priority order.

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware and software. In thisconnection a user terminal (mobile terminal) and an eNodeB (basestation) are provided. The user terminal and base station is adapted toperform the methods described herein, including corresponding entitiesto participate appropriately in the methods, such as receiver,transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. The various embodiments may also be performed or embodied by acombination of these devices.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,flash memory, registers, hard disks, CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

Summarizing, the present disclosure relates to a method to be performedat a user equipment and to a user equipment operable in a wirelesscommunications system supporting direct communication between userequipments. Accordingly, a sidelink configuration is stored in the userequipment, specifying a plurality of destination groups, eachdestination group including possible destinations for sidelink data aswell a logical channel priority is stored for each logical channel outof logical channels configured for the sidelink destination groups. Theterminal then selects a sidelink destination group with a sidelinklogical channel having sidelink data available for transmission with thehighest logical channel priority among the sidelink logical channelshaving data available for transmission, and allocates radio resources tothe sidelink logical channels belonging to the selected sidelinkdestination group in decreasing priority order.

What is claimed is:
 1. A user equipment operable in a wirelesscommunications system supporting direct communication between userequipments, comprising: circuitry, which, in operation: selects asidelink destination group (ProSe destination) associated with asidelink logical channel having a highest logical channel priority amongsidelink logical channels, which have data available for transmission ina sidelink control period (SC period) and which have not previously beenselected in the same sidelink control period, wherein each of thesidelink logical channels belongs to a sidelink destination group, eachof the sidelink logical channels is allocated to a logical channel group(LCG) depending on a priority of said each sidelink logical channel andon a priority of the logical channel group, and the logical channelgroup is defined per sidelink destination group; and allocates radioresources to sidelink logical channels belonging to the selectedsidelink destination group in decreasing priority order; and atransmitter, which, in operation, transmits the data using the allocatedradio resources.
 2. The user equipment according to claim 1, wherein thelogical channel priority depends on at least one factor chosen from: adestination group priority associated with the sidelink destinationgroup; a logical channel group priority associated with a group oflogical channels, grouped according to a data type; a geographicallocation of the user equipment; an emergency level in which the userequipment is operating; and a user equipment identifier.
 3. The userequipment according to claim 1, further comprising: a receiver, which,in operation, receives an indication of logical channel priorities ofthe respective logical channels determined by a ProSe (proximityservices) function in a ProSe entity of the wireless communicationssystem, and stores the logical priorities.
 4. The user equipmentaccording to claim 1, wherein the circuitry, in operation, determines alogical channel priority of a logical channel.
 5. The user equipmentaccording to claim 1, further comprising: a buffer, which, in operation,stores data to be transmitted for a logical channel; wherein, thecircuitry, in operation, modifies a current priority of said logicalchannel into a modified priority either based on own recalculation ofthe priority or based on a command received from a ProSe function. 6.The user equipment according to claim 5, wherein the data stored in thebuffer before modification are either flushed or transmitted with thecurrent priority depending on at least one factor chosen from: acomparative determination of whether the current priority is higher thanthe modified priority; a level of the modified priority; and a cause ofthe modification.
 7. The user equipment according to claim 1, whereinthe circuitry, in operation: determines that the user equipment isselected or not selected to transmit data among the user equipments ofthe wireless communications system; responsive to determining that theuser equipment is not selected, suspends sidelink logical channelsassociated with the user equipment and does not select or allocateresources to the suspended sidelink logical channels; and responsive todetermining that the user equipment is selected, resumes the sidelinklogical channels which were previously suspended.
 8. The user equipmentaccording to claim 7, wherein the circuitry, in operation: determinesthat the user equipment is not to transmit data, according to messagesexchanged in the wireless communications system between the userequipments and/or a proximity service entity in a layer above MAC(medium access control), and responsive to determining that the userequipment is not to transmit data, stops transmission of data and/orsidelink control information.
 9. The user equipment according to claim7, wherein the circuitry, in operation: extracts, from sidelink controlinformation on physical layer or a MAC (medium access control) PDU(protocol data unit), received from another user equipment, a userequipment priority indicator; compares the extracted user equipmentpriority indicator with an own user equipment priority stored in theuser equipment or a priority of the data to be transmitted; andresponsive to the own user equipment priority being lower than theextracted user equipment priority indicator, determines that the userequipment is not selected to transmit data.
 10. The user equipmentaccording to claim 9, wherein, responsive to the user equipment having afloor and receiving sidelink control information from another userequipment with a higher user equipment priority, the circuitry stopstransmission of the data via the transmitter.
 11. The user equipmentaccording to claim 9, wherein the user equipment priority indicator iscarried within a MAC header of the MAC PDU and is configured by a ProSe(proximity services) entity of the wireless communications system. 12.The user equipment according to claim 1, wherein the circuitry, inoperation, reports to a network node of the wireless communicationssystem a status of a buffer associated with a logical channel priority.13. The user equipment according to claim 1, wherein the circuitry, inoperation, selects the radio resources to be allocated from a resourcepool, and selects the resource pool among a plurality of resource poolsaccording to a priority associated with the selected sidelinkdestination group or a logical channel priority associated with alogical channel from which the data is to be transmitted.
 14. A methodperformed at a user equipment operable in a wireless communicationssystem supporting direct communication between user equipments, themethod comprising: selecting a sidelink destination group (ProSedestination) associated with a sidelink logical channel having a highestlogical channel priority among sidelink logical channels, which havedata available for transmission in a sidelink control period (SC period)and have not previously been selected in the same sidelink controlperiod, wherein each of the sidelink logical channels belongs to asidelink destination group, each of the sidelink logical channels isallocated to a logical channel group (LCG) depending on a priority ofsaid each sidelink logical channel and on a priority of the logicalchannel group, and the logical channel group is defined per sidelinkdestination group; allocating radio resources to sidelink logicalchannels belonging to the selected sidelink destination group indecreasing priority order; and transmitting the data using the allocatedradio resources.